Display device, electronic device, and mobile information terminal

ABSTRACT

A display device capable of displaying images with wide color gamut is provided. A display device capable of displaying images with wide color gamut and capable of relaxing contrast made by narrow spectra is provided. The display device includes a liquid crystal element and a light-emitting element. Light obtained from the liquid crystal element through a color filter has an NTSC area ratio of more than or equal to 20 percent and less than or equal to 60 percent and light emitted by the light-emitting element has a BT.2020 area ratio of more than or equal to 80 percent and less than or equal to 100 percent.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device andan electronic device. Note that one embodiment of the present inventionis not limited thereto. That is, one embodiment of the present inventionrelates to an object, a method, a manufacturing method, or a drivingmethod. In addition, one embodiment of the present invention relates toa process, a machine, manufacture, and a composition of matter. Asspecific examples, a semiconductor device, a display device, a liquidcrystal display device, a lighting device, and the like can be given.

BACKGROUND ART

As display devices, liquid crystal display devices including a liquidcrystal element as their display element, light-emitting devicesincluding a light-emitting element (EL element) as their displayelement, and the like are known. For example, in a liquid crystaldisplay device, a liquid crystal element including a liquid crystalmaterial is interposed between a pair of electrodes facing each otherwith alignment films provided between the liquid crystal element and theelectrodes, and the liquid crystal display device displays images byutilizing the optical modulation action of the liquid crystal. Alight-emitting device includes a light-emitting element in which an ELlayer is interposed between a pair of electrodes, and displays images byutilizing light emission obtained from the light-emitting element whenvoltage is applied between the pair of electrodes.

In order to perform full-color display with the use of the displayelements, in the case of the liquid crystal element, a color filter isused in combination with the liquid crystal element, whereby full-colordisplay can be performed. In the case of the light-emitting element, aplurality of light-emitting elements in which EL layers includelight-emitting materials for different light emission colors are formed,whereby full-color display can be performed. Alternatively, the lightemitting element can also be used in combination with a color filter.

As specific methods for displaying full-color images with light-emittingelements, so-called side-by-side patterning in which light-emittingelements which emit light of different colors are separately formed, awhite-color filter method in which a white color light-emitting elementis combined with a color filter, and a color conversion method in whicha light-emitting element which emits monochromatic light such as a bluelight-emitting element is combined with a color conversion filter can begiven.

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2007-53090 DISCLOSURE OF INVENTION

In order to make such a display device display full-color images, thechromaticities (x, y) of emission colors of light-emitting elements areset within desired ranges, so that images with wide color gamut can bedisplayed.

However, although light emitted by a light-emitting element has anexcellent chromaticity, the light has extremely narrow spectra, suchthat the display has strong contrast, and thus is too intense for theviewers and likely to tire them.

Then, one embodiment of the present invention provides a display devicecapable of displaying images with wide color gamut. Another embodimentof the present invention provides a display device capable of displayingimages with wide color gamut and capable of relaxing contrast made bynarrow spectra. Another embodiment of the present invention provides adisplay device capable of displaying eye-friendly images with wide colorgamut. Another embodiment of the present invention provides a novellight-emitting element. Another embodiment of the present inventionprovides a light-emitting element with excellent color purity.

Note that the descriptions of these objects do not preclude theexistence of other objects. In one embodiment of the present invention,there is no need to achieve all the objects. Other objects will beapparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

One embodiment of the present invention is a display device including aliquid crystal element and a light-emitting element. In the displaydevice, light obtained from the liquid crystal element through a colorfilter has an NTSC area ratio of more than or equal to 20% and less thanor equal to 60% and light emitted by the light-emitting element has aBT.2020 area ratio of more than or equal to 80% and less than or equalto 100%. Note that the light emitted by the light-emitting elementpreferably has a BT.2020 area ratio of more than or equal to 90% andless than or equal to 100%.

Another embodiment of the present invention is a display deviceincluding a liquid crystal element and a light-emitting element. In thedisplay device, light obtained from the liquid crystal element through acolor filter has an NTSC coverage of more than or equal to 20% and lessthan or equal to 60% and light emitted by the light-emitting element hasa BT.2020 coverage of more than or equal to 75% and less than or equalto 100%. Note that the light emitted by the light-emitting elementpreferably has a BT.2020 coverage of more than or equal to 75% and lessthan or equal to 100%.

Another embodiment of the present invention is a display deviceincluding a liquid crystal element and a light-emitting element. In thedisplay device, light obtained from the liquid crystal element has anNTSC coverage of more than or equal to 20% and less than or equal to 60%and light emitted by the light-emitting element has CIE 1931chromaticity coordinates (x, y), where x is more than or equal to 0.130and less than or equal to 0.250 and y is more than 0.710 and less thanor equal to 0.810.

Another embodiment of the present invention is a display deviceincluding a liquid crystal element and a light-emitting element. In thedisplay device, light obtained from the liquid crystal element has anNTSC coverage of more than or equal to 20% and less than or equal to 60%and light emitted by the light-emitting element has CIE 1931chromaticity coordinates (x, y), where x is more than 0.680 and lessthan or equal to 0.720 and y is more than or equal to 0.260 and lessthan or equal to 0.320.

Another embodiment of the present invention is a display deviceincluding a liquid crystal element and a light-emitting element. In thedisplay device, light obtained from the liquid crystal element has anNTSC coverage of more than or equal to 20% and less than or equal to 60%and light emitted by the light-emitting element has CIE 1931chromaticity coordinates (x, y), where x is more than or equal to 0.120and less than or equal to 0.170 and y is more than or equal to 0.020 andless than 0.060.

Note that, in each of the above structures, the liquid crystal elementis a reflective liquid crystal element and the light-emitting element isa light-emitting element including an EL layer between a reflectiveelectrode and a semi-transmissive and semi-reflective electrode.

In the above structures, the EL layer included in the light-emittingelement preferably emits white light. The EL layer includes at least alight-emitting layer. A plurality of EL layers may be provided. The ELlayers may be stacked with a charge generation layer providedtherebetween.

Another embodiment of the present invention is an electronic device thatincludes the display device of one embodiment of the present inventionand an operation key, a speaker, a microphone, or an external connectionportion.

Another embodiment of the present invention is a mobile informationterminal that includes the display device of one embodiment of thepresent invention and an operation key, a speaker, a microphone, or anexternal connection portion.

One embodiment of the present invention includes, in its category, inaddition to a display device including a display element, an electronicdevice including the display device (specifically, an electronic deviceincluding the display element or the display device and a connectionterminal or an operation key) and a lighting device including thedisplay device (specifically, a lighting device including the displayelement or the display device and a housing). Accordingly, a displaydevice in this specification means an image display device or a lightsource (including a lighting device). Furthermore, the display deviceincludes the following modules in its category: a module in which aconnector such as a flexible printed circuit (FPC) or a tape carrierpackage (TCP) is attached to a display device; a module having a TCPwhose end is provided with a printed wiring board; and a module in whichan integrated circuit (IC) is directly mounted on a display element by achip on glass (COG) method.

According to one embodiment of the present invention, a display devicecapable of displaying images with wide color gamut can be provided.According to another embodiment of the present invention, a displaydevice capable of displaying images with wide color gamut and capable ofrelaxing contrast made by narrow spectra can be provided. According toanother embodiment of the present invention, a display device capable ofdisplaying eye-friendly images with wide color gamut can be provided.According to another embodiment of the present invention, a novellight-emitting element can be provided. According to another embodimentof the present invention, a light-emitting element with excellent colorpurity can be provided.

Note that the description of these effects does not preclude theexistence of other effects. One embodiment of the present invention doesnot necessarily achieve all the effects listed above. Other effects willbe apparent from and can be derived from the description of thespecification, the drawings, the claims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams illustrating a display device of oneembodiment of the present invention;

FIGS. 2A to 2C are diagrams each illustrating a display device of oneembodiment of the present invention;

FIGS. 3A to 3D are diagrams each illustrating a display device of oneembodiment of the present invention;

FIGS. 4A to 4E are diagrams each illustrating a display device of oneembodiment of the present invention;

FIGS. 5A, 5B1, and 5B2 are diagrams each illustrating a display deviceof one embodiment of the present invention;

FIG. 6 is a diagram illustrating a display device of one embodiment ofthe present invention;

FIGS. 7A to 7D, 7D′-1, 7D′-2, and 7E are diagrams each illustrating anelectronic device;

FIGS. 8A to 8C are diagrams illustrating an electronic device;

FIGS. 9A and 9B are diagrams illustrating an automobile;

FIG. 10 is a diagram showing an NTSC coverage-reflectance characteristic(simulated values) of a liquid crystal panel;

FIG. 11 is a diagram showing an NTSC coverage-reflectance characteristic(actual values) of a liquid crystal panel;

FIG. 12 is a diagram showing an NTSC coverage-reflectance characteristicof a liquid crystal panel (corrected values);

FIG. 13 is a diagram illustrating a light-emitting element;

FIG. 14 shows transmission spectra of color filters;

FIG. 15 is a diagram showing a luminance-current density characteristicof light-emitting elements 1 to 4;

FIG. 16 is a diagram showing a luminance-voltage characteristic oflight-emitting elements 1 to 4;

FIG. 17 is a diagram showing a current efficiency-luminancecharacteristic of light-emitting elements 1 to 4;

FIG. 18 is a diagram showing a current-voltage characteristic oflight-emitting elements 1 to 4;

FIG. 19 shows light emission spectra of light-emitting elements 1 to 4;

FIG. 20 is a diagram showing a luminance-current density characteristicof light-emitting elements 5 to 8;

FIG. 21 is a diagram showing a luminance-voltage characteristic oflight-emitting elements 5 to 8;

FIG. 22 is a diagram showing a current efficiency-luminancecharacteristic of light-emitting elements 5 to 8;

FIG. 23 is a diagram showing a current-voltage characteristic oflight-emitting elements 5 to 8; and

FIG. 24 shows light emission spectra of light-emitting elements 5 to 8.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings. However, the present invention is not limitedto the following description, and the mode and details can be variouslychanged unless departing from the scope and spirit of the presentinvention. Thus, the present invention should not be construed as beinglimited to the description in the following embodiments.

Note that the position, the size, the range, or the like of eachstructure illustrated in the drawings and the like are not accuratelyrepresented in some cases for easy understanding. Therefore, thedisclosed invention is not necessarily limited to the position, size,range, or the like as disclosed in the drawings and the like.

In describing the structures of the invention with reference to thedrawings in this specification and the like, common reference numeralsare used for the same portions in different drawings.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention will be described with reference to FIGS. 1A and 1B.

FIG. 1A illustrates a structure of a display device of one embodiment ofthe present invention, which includes a liquid crystal element 100L anda light-emitting element 100E.

The liquid crystal element 100L includes a liquid crystal layer 103L andalignment films 104 between a first electrode 101L and a secondelectrode 102L. The first electrode 101L is a reflective electrode whichcan reflect ambient light. The second electrode 102L is a transparentelectrode that has a light-transmitting property and is capable oftransmitting visible light.

A color filter (also referred to as a coloring layer) 105L and apolarizing layer 106 are provided on the side where light transmittedthrough the second electrode 102L exits to the outside. Accordingly, thelight transmitted through the second electrode 102L is transmittedthrough the color filter 105L and the polarizing layer 106 to becomelight 107L.

The light-emitting element 100E includes an EL layer 103E between afirst electrode 101E and a second electrode 102E. Note that at least oneof electrodes included in the light-emitting element, the secondelectrode 102E, is a transparent electrode that has a light-transmittingproperty and is capable of transmitting visible light. The EL layer 103Ecan contain a light-emitting material from which a desirable lightemission color can be obtained or can contain a plurality oflight-emitting materials of different light emission colors incombination. A color filter (also referred to as a coloring layer) 105Eis provided as needed on the side where light transmitted through thesecond electrode 102E is emitted outward.

The light emitted by the EL layer 103E is transmitted through the secondelectrode 102E and transmitted through the color filter 105E, if thecolor filter 105E is provided, to become light 107E.

The display device in this embodiment includes the liquid crystalelement 100L and the light-emitting element 100E; thus, light obtainedfrom the display device is light 108 including the light 107L exitingfrom the liquid crystal element 100L and the light 107E emitted by thelight-emitting element 100E.

Note that light exiting from the liquid crystal element 100L (the light107L) in the display device in this embodiment meets the NationalTelevision System Committee (NTSC) standard among quality indicators forfull-color display. The NTSC standard is a color gamut standard foranalog television and was established by the NTSC. The NTSC standardcolor gamut is shown in FIG. 1B. Specifically, the light 107L has afull-color display quality that meets chromaticity coordinates (x, y),in the CIE 1931 chromaticity coordinates (xy chromaticity coordinates),of red (R) at (0.670, 0.330); green (G), (0.210, 0.710); and blue (B),(0.140, 0.080). The CIE 1931 chromaticity coordinates are provided bythe International Commission on Illumination (CIE). Note that an NTSCarea ratio is obtained in the following manner: an area P of a triangleformed by connecting the CIE 1931 chromaticity coordinates of R, G, andB which fulfill the NTSC standard (the above xy chromaticitycoordinates) and an area Q of a triangle formed by connecting the CIEchromaticity coordinates (x, y) of the liquid crystal elements (R, G,and B) of one embodiment of the present invention are calculated andthen the area ratio (Q/P) is calculated. An NTSC coverage is a valuewhich represents how much percentage of the NTSC standard color gamut(the inside of the above triangle) can be reproduced using a combinationof the CIE chromaticity coordinates (x, y) of the liquid crystalelements (R, G, and B) of one embodiment of the present invention.

In this embodiment, a reflective liquid crystal element is preferablyused as the liquid crystal element 100L included in the display device.In the liquid crystal element 100L, an NTSC area ratio or an NTSCcoverage is preferably more than or equal to 20% and less than or equalto 60%. This is because a reflectance of more than or equal to 15% canbe obtained in a panel including a reflective liquid crystal elementwhen the NTSC area ratio or an NTSC coverage of the liquid crystalelement 100L is more than or equal to 20% and less than or equal to 60%.The display device in this embodiment is a panel including alight-emitting element capable of meeting BT.2020 and a liquid crystalelement. Therefore, when the liquid crystal element has an NTSC arearatio or an NTSC coverage of more than or equal to 20% and less than orequal to 60% and a panel including the liquid crystal element is sobright as to have a reflectance of more than or equal to 15%, thedisplay device, as a whole, can display eye-friendly images with widecolor gamut and high visibility. Note that to examine the relation ofthe reflectance to the NTSC area ratio or coverage in the panelincluding a reflective liquid crystal element, simulation results willbe described in Examples.

When a reflective liquid crystal element is used as the liquid crystalelement 100L included in the display device, eye-friendly images can bedisplayed because the viewers seeing images displayed by the liquidcrystal element do not directly see the light source of the element (thelight source is an indirect light source). Note that when the viewerscan see the display without directly seeing the light source in theabove manner, a transmissive liquid crystal element, a MEMS element, orthe like can also be used.

As a driving mode for the liquid crystal element 100L, a verticalalignment (VA) mode, a twisted nematic (TN) mode, an in-plane-switching(IPS) mode, a fringe field switching (FFS) mode, an opticallycompensated birefringence (OCB) mode, a blue phase, or the like can beused. Note that as a specific example of the VA mode, a multi-domainvertical alignment (MVA) mode, a patterned vertical alignment (PVA)mode, an electrically controlled birefringence (ECB) mode, a continuouspinwheel alignment (CPA) mode, an advanced super view (ASV) mode, or thelike can be given.

As the liquid crystal used for the liquid crystal element 100L, athermotropic liquid crystal, a low-molecular liquid crystal, ahigh-molecular liquid crystal, a polymer dispersed liquid crystal(PDLC), a ferroelectric liquid crystal, an anti-ferroelectric liquidcrystal, or the like can be used. Such a liquid crystal exhibits acholesteric phase, a smectic phase, a cubic phase, a chiral nematicphase, an isotropic phase, or the like depending on conditions. Inaddition, either a positive liquid crystal or a negative liquid crystalmay be used, and an appropriate liquid crystal material can be useddepending on the mode or design to be used.

For materials used for the electrodes of the liquid crystal element 100L(the first electrode 101L and the second electrode 102L), any of thematerials below can be used in an appropriate combination as long as theabove functions (e.g., a light-transmitting property) can be fulfilled.For example, a metal, an alloy, an electrically conductive compound, amixture of these, and the like can be appropriately used. Specifically,an In—Sn oxide (also referred to as ITO), an In—Si—Sn oxide (alsoreferred to as ITSO), an In—Zn oxide, an In—W—Zn oxide, or the like canbe used. In addition, it is possible to use a metal such as aluminum(Al), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), gallium (Ga), zinc (Zn), indium (In),tin (Sn), zirconium (Zr), molybdenum (Mo), tantalum (Ta), tungsten (W),palladium (Pd), gold (Au), platinum (Pt), silver (Ag), yttrium (Y), orneodymium (Nd) or an alloy containing an appropriate combination of anyof these metals. It is also possible to use a Group 1 element or a Group2 element in the periodic table, which is not described above (e.g.,lithium (Li), cesium (Cs), calcium (Ca), or strontium (Sr)), a rareearth metal such as europium (Eu) or ytterbium (Yb), an alloy containingan appropriate combination of any of these elements, graphene, or thelike.

The color filter 105E and the color filter 105L are each a filter thattransmits visible light in a specific wavelength range and blocksvisible light in a specific wavelength range. Thus, when the colorfilters 105E and 105L transmitting only light in a desired wavelengthrange are provided appropriately, colors of light exiting from theliquid crystal element can be adjusted. Note that the color filters 105Eand 105L can be formed by a staining method, a pigment dispersionmethod, a printing method, an evaporation method, and the like.

The polarizing layer 106 is a filter that lets light having limitedvibration directions pass through the polarizing layer 106. Thepolarizing layer 106 may be provided on the inner side of the substrateplaced outside the electrodes of the liquid crystal element 100L (thefirst electrode 101L and the second electrode 102L) (on the side closeto the electrodes) or may be provided on the outer side of thesubstrate. Although not illustrated in FIG. 1A, a retardation layer maybe provided.

In addition, light emitted by the light-emitting element 100E (the light107E) in the display device of one embodiment of the present inventionpreferably has a chromaticity (x, y) that meets a standard establishedby Japan Broadcasting Corporation (NHK) and used for ultra highdefinition television (UHDTV, also referred to as Super Hi-Visiontelevision) among quality indicators for full-color display. Thestandard is so-called BT.2020 standard. The BT.2020 standard color gamutis shown in FIG. 1B. Specifically, the BT.2020 standard meets afull-color display quality that meets chromaticity coordinates (x, y),in the CIE 1931 chromaticity coordinates (xy chromaticity coordinates),of red at (0.708, 0.292); green, (0.170, 0.797); and blue, (0.131,0.046). The CIE 1931 chromaticity coordinates are established by theInternational Commission on Illumination (CIE).

For materials used for the electrodes of the light-emitting element 100E(the first electrode 101E and the second electrode 102E), the materialsdescribed above as the materials used for the electrodes of the liquidcrystal element 100L (the first electrode 101L and the second electrode102L) can be used in an appropriate combination as long as the abovefunctions (e.g., transmittance) can be fulfilled.

The light-emitting elements meeting the BT.2020 standard include alight-emitting element (red) 200R which emits red light, alight-emitting element (green) 200G which emits green light, and alight-emitting element (blue) 200B which emits blue light as illustratedin FIG. 2A. These light-emitting elements can include respective ELlayers (203R, 203G, and 203B) which include different light-emittingmaterials. Note that stack structures and materials of the EL layers arepreferably selected such that the chromaticity (x, y) of thelight-emitting element (red) 200R is (0.708, 0.292), the chromaticity ofthe light-emitting element (green) 200G is (0.170, 0.797), and thechromaticity of the light-emitting element (blue) 200B is (0.131,0.046).

Note that the light-emitting elements (200R, 200G, and 200B) in FIG. 2Aeach include a first electrode 201 and a second electrode 202. In thecase of the light-emitting elements (200R, 200G, and 200B) in FIG. 2A, atransparent electrode which transmits visible light is used at least asthe second electrode 202. In addition, red light 207R is emitted by theEL layer 203R in the light-emitting element (red) 200R, green light 207Gis emitted by the EL layer 203G in the light-emitting element (green)200G, and blue light 207B is emitted by the EL layer 203B in thelight-emitting element (blue) 200B.

Light-emitting elements having the structures illustrated in FIG. 2B arealso formed so as to meet the BT.2020 standard. Each of thelight-emitting elements in FIG. 2B is identical to each of thelight-emitting elements in FIG. 2A in the structure of the firstelectrode 201 and the second electrode 202, and is different in that alight-emitting element (red) 200R′, a light-emitting element (green)200G′, and a light-emitting element (blue) 200B′ includes a common ELlayer 203W which emits white light. Note that red light 207R′ isobtained from the light-emitting element (red) 200R′ by passing througha color filter (red) 204R having a function of transmitting red light.In addition, green light 207G′ is obtained from the light-emittingelement (green) 200G′ by passing through a color filter (green) 204Ghaving a function of transmitting green light. Furthermore, blue light207B′ is obtained from the light-emitting element (blue) 200B′ bypassing through a color filter (blue) 204B having a function oftransmitting blue light.

Light-emitting elements having the structures illustrated in FIG. 2C arealso formed so as to meet the BT.2020 standard. The light-emittingelements having the structures illustrated in FIG. 2C are preferable forforming light-emitting elements meeting the BT.2020 standard because thelight-emitting elements in FIG. 2C have a micro optical resonator(microcavity) structure having a function of strengthening lightemission depending on colors of the light to be obtained from thelight-emitting elements. Accordingly, in the light-emitting elements inFIG. 2C, the first electrode 201 is a reflective electrode and a secondelectrode 202′ is a semi-transmissive and semi-reflective electrode.Note that even light-emitting elements including the separately formedEL layers as illustrated in FIG. 2A can be combined with a micro opticalresonator (microcavity) structure.

In FIG. 2C, a light-emitting element (red) 200R″ is a light-emittingelement which emits red light; thus, it is preferable that alight-transmitting conductive film 208R be stacked over the firstelectrode 201 and an optical path length between the first electrode 201and the second electrode 202′ be adjusted so as to be an optical pathlength a, which is suitable for strengthening red light emission. Inaddition, a light-emitting element (green) 200G″ is a light-emittingelement which emits green light; thus, it is preferable that alight-transmitting conductive film 208G be stacked over the firstelectrode 201 and the optical path length between the first electrode201 and the second electrode 202′ be adjusted so as to be an opticalpath length b, which is suitable for strengthening green light emission.Furthermore, a light-emitting element (blue) 200B″ is a light-emittingelement which emits blue light; therefore, the EL layer 203W is formedsuch that the optical path length between the first electrode 201 andthe second electrode 202′ becomes an optical path length c, which issuitable for strengthening blue light emission. As needed, alight-transmitting conductive film can be stacked over the firstelectrode 201 to adjust the optical path length.

When white light is emitted from the EL layer 203W as illustrated inFIGS. 2B and 2C, it is desirable that red, green, and blue lightemission, which compose white light emission, each have an independentlight emission spectrum. The spectra desirably do not overlap with eachother in order to prevent the decrease in the color purity. The spectraof specifically green light emission and red light emission have peakwavelengths close to each other and are likely to overlap with eachother. In order to prevent such overlap of light emission spectra, afavorable light-emitting material is used for the EL layer included inthe EL layer 203W and a specific stack structure is employed in thelight-emitting element described in this embodiment. Thus, overlap ofdifferent light emission spectra can be prevented, so thatlight-emitting elements which show excellent color chromaticities forevery color can be obtained.

As the light-emitting element 100E included in the display device inthis embodiment, light-emitting elements which cover chromaticity ranges(a region A, a region B, and a region C) represented in the chromaticitycoordinates in FIG. 1B are preferably used. As specific chromaticityranges for the light-emitting elements, the light-emitting element (red)(200R, 200R′, or 200R″) covers a chromaticity range represented by theregion A, the light-emitting element (green) (200G, 200G′, or 200G″)covers a chromaticity range represented by the region B, and thelight-emitting element (blue) (200B, 200B′, or 200B″) covers achromaticity range represented by the region C. In the CIE 1931chromaticity coordinates, the region A has x of more than 0.680 and lessthan or equal to 0.720 and y of more than or equal to 0.260 and lessthan or equal to 0.320, the region B has x of more than or equal to0.130 and less than or equal to 0.250 and y of more than 0.710 and lessthan or equal to 0.810, and the region C has x of more than or equal to0.120 and less than or equal to 0.170 and y of more than or equal to0.020 and less than 0.060.

Note that the peak wavelength of the light emission spectrum of each ofthe light-emitting elements (red) (200R, 200R′, and 200R″) in FIGS. 2Ato 2C is preferably more than or equal to 620 nm and less than or equalto 680 nm. In addition, the peak wavelength of the light emissionspectrum of each of the light-emitting elements (green) (200G, 200G′,and 200G″) is preferably more than or equal to 500 nm and less than orequal to 530 nm. Furthermore, the peak wavelength of the light emissionspectrum of each of the light-emitting elements (blue) (200B, 200B′, and200B″) is preferably more than or equal to 430 nm and less than or equalto 460 nm. The half widths of the light emission spectra of thelight-emitting element (red) (200R, 200R′, or 200R″), the light-emittingelement (green) (200G, 200G′, or 200G″), and the light-emitting element(blue) (200B, 200B′, or 200B″) are preferably more than or equal to 5 nmand less than or equal to 45 nm, more than or equal to 5 nm and lessthan or equal to 35 nm, and more than or equal to 5 nm and less than orequal to 25 nm, respectively.

In one embodiment of the present invention, light emitted by thelight-emitting element preferably meets the above chromaticity, and thearea ratio thereof to the BT.2020 color gamut in the CIE chromaticitycoordinates (x, y) is preferably more than or equal to 80% or thecoverage of the BT.2020 color gamut is preferably more than or equal to75%. Further preferably, the area ratio is more than or equal to 90% orthe coverage is more than or equal to 85%.

Accordingly, in the display device in this embodiment, light exitingfrom the liquid crystal element through a color filter has an NTSC arearatio or an NTSC coverage of more than or equal to 20% and less than orequal to 60%, and light emitted by the light-emitting element has aBT.2020 area ratio of more than or equal to 80% and less than or equalto 100% or a BT.2020 coverage of more than or equal to 75% and less thanor equal to 100%. Note that the light emitted by the light-emittingelement further preferably has a BT.2020 area ratio of more than orequal to 90% and less than or equal to 100% or a BT.2020 coverage ofmore than or equal to 85% and less than or equal to 100%.

Note that in order to calculate the chromaticity, any of a luminancecolorimeter, a spectroradiometer, and an emission spectrometer may beused, and it is sufficient that the above chromaticity be met by any oneof the measuring methods. However, it is further preferable that theabove chromaticity be met by all of the measuring methods.

Note that the structure described in this embodiment can be used in anappropriate combination with any of the structures described in theother embodiments.

Embodiment 2

In this embodiment, an example of a light-emitting element which can beapplied to a display device of one embodiment of the present inventionwill be described.

<<Basic Structure of Light-Emitting Element>>

A basic structure of a light-emitting element will be described. FIG. 3Aillustrates a light-emitting element in which an EL layer including alight-emitting layer is provided between a pair of electrodes.Specifically, an EL layer 303 is provided between a first electrode 301and a second electrode 302.

FIG. 3B illustrates a light-emitting element that has a stacked-layerstructure (tandem structure) in which a plurality of EL layers (two ELlayers 303 a and 303 b in FIG. 3B) are provided between a pair ofelectrodes and a charge generation layer 304 is provided between the ELlayers. Such a tandem light-emitting element can be driven at lowvoltage.

The charge generation layer 304 has a function of injecting electronsinto one of the EL layers (303 a or 303 b) and injecting holes into theother of the EL layers (303 b or 303 a) when a voltage is appliedbetween the first electrode 301 and the second electrode 302. Thus, inFIG. 3B, when a voltage is applied between the first electrode 301 andthe second electrode 302 such that the potential of the first electrode301 is higher than that of the second electrode 302, the chargegeneration layer 304 injects electrons into the EL layer 303 a andinjects holes into the EL layer 303 b.

Note that in terms of light extraction efficiency, the charge generationlayer 304 preferably has a property of transmitting visible light(specifically, the charge generation layer 304 has a visible lighttransmittance of 40% or higher). Furthermore, the charge generationlayer 304 functions even if it has lower conductivity than the firstelectrode 301 or the second electrode 302.

FIG. 3C illustrates the EL layer 303 of the light-emitting elementhaving a stacked-layer structure. In this case, the first electrode 301is regarded as functioning as an anode. The EL layer 303 has a structurein which a hole-injection layer 311, a hole-transport layer 312, alight-emitting layer 313, an electron-transport layer 314, and anelectron-injection layer 315 are stacked in this order over the firstelectrode 301. Even in the case where a plurality of EL layers areprovided as in the tandem structure illustrated in FIG. 3B, the layersin each EL layer are sequentially stacked from the anode side asdescribed above. When the first electrode 301 is a cathode and thesecond electrode 302 is an anode, the stacking order of the layers isreversed.

The light-emitting layer 313 included in the EL layers (303, 303 a, and303 b) contains an appropriate combination of a light-emitting materialand a plurality of materials, so that fluorescence or phosphorescence ofa desired light emission color can be obtained. The light-emitting layer313 may include a stacked-layer structure having different lightemission colors. In that case, the light-emitting material and othermaterials are different between the stacked light-emitting layers.Alternatively, the plurality of EL layers (303 a and 303 b) in FIG. 3Bmay exhibit the respective light emission colors. Also in that case, thelight-emitting material and other materials are different between thelight-emitting layers.

As one embodiment of the present invention, the light-emitting elementin FIG. 3C has, for example, a micro optical resonator (microcavity)structure in which the first electrode 301 is a reflective electrode andthe second electrode 302 is a semi-transmissive and semi-reflectiveelectrode, whereby light emission from the light-emitting layer 313 inthe EL layer 303 can be resonated between the electrodes. Thus, lightemission obtained through the second electrode 302 can be intensified.

Note that when the first electrode 301 of the light-emitting element isa reflective electrode with a structure in which a reflective conductivematerial and a light-transmitting conductive material (a transparentconductive film) are stacked, optical adjustment can be performed bycontrolling the thickness of the transparent conductive film.Specifically, when the wavelength of light from the light-emitting layer313 is λ, the distance between the first electrode 301 and the secondelectrode 302 is preferably adjusted to around mλ/2 (m is a naturalnumber).

To amplify desired light (wavelength: λ) obtained from thelight-emitting layer 313, the optical path length from the firstelectrode 301 to a region in the light-emitting layer 313 emitting thedesired light (light-emitting region) and the optical path length fromthe second electrode 302 to the region in the light-emitting layer 313emitting the desired light (light-emitting region) are each preferablyadjusted to around (2m′+1)λ/4 (m′ is a natural number). Here, thelight-emitting region means a region where holes and electrons arerecombined in the light-emitting layer 313.

By such optical adjustment, the spectrum of specific monochromatic lightfrom the light-emitting layer 313 can be narrowed and light emissionwith a high color purity can be obtained.

In that case, the optical path length between the first electrode 301and the second electrode 302 is, to be exact, represented by the totalthickness from a reflective region in the first electrode 301 to areflective region in the second electrode 302. However, it is difficultto precisely determine the reflective region in the first electrode 301or the second electrode 302; therefore, it is presumed that the aboveeffect can be sufficiently obtained when appropriate positions in thefirst electrode 301 and the second electrode 302 are assumed to be thereflective regions. Furthermore, the optical path length between thefirst electrode 301 and the light-emitting layer emitting desired lightis, to be exact, the optical path length between the reflective regionin the first electrode 301 and the light-emitting region in thelight-emitting layer emitting desired light. However, it is difficult toprecisely determine the reflective region in the first electrode 301 orthe light-emitting region in the light-emitting layer emitting desiredlight; therefore, it is presumed that the above effect can besufficiently obtained when appropriate positions in the first electrode301 are assumed to be the reflective regions and appropriate positionsin the light-emitting layer emitting desired light are assumed to be thelight-emitting regions.

The light-emitting element in FIG. 3C has a microcavity structure, sothat light (monochromatic light rays) with different wavelengths can beextracted even if the same EL layer is employed. Thus, separate coloringaimed at plural light emission colors (e.g., R, G, and B) is notnecessary. Therefore, higher-resolution display can be easily achieved.Note that a combination with color filters is also possible.Furthermore, light emission intensity with a specific wavelength in thefront direction can be increased, whereby power consumption can bereduced.

In the above light-emitting element, at least one of the first electrode301 and the second electrode 302 is a light-transmitting electrode (atransparent electrode, a semi-transmissive and semi-reflectiveelectrode, or the like). In the case where the light-transmittingelectrode is a transparent electrode, the transparent electrode has avisible light transmittance of more than or equal to 40%. In the casewhere the light-transmitting electrode is a semi-transmissive andsemi-reflective electrode, the semi-transmissive and semi-reflectiveelectrode has a visible light reflectance of more than or equal to 20%and less than or equal to 80%, preferably more than or equal to 40% andless than or equal to 70%. These electrodes preferably have aresistivity of 1×10⁻² Ωcm or less.

Furthermore, when one of the first electrode 301 and the secondelectrode 302 is a reflective electrode in the above light-emittingelement, the visible light reflectance of the reflective electrode ismore than or equal to 40% and less than or equal to 100%, preferablymore than or equal to 70% and less than or equal to 100%. This electrodepreferably has a resistivity of 1×10⁻² Ωcm or less.

<<Specific Structure and Forming Method of Light-Emitting Element>>

Next, a specific structure and a specific forming method of thelight-emitting element will be described. Here, a light-emitting elementhaving the tandem structure in FIG. 3B and microcavity structures isdescribed with reference to FIG. 3D. In the light-emitting element inFIG. 3D, a reflective electrode is formed as the first electrode 301 anda semi-transmissive and semi-reflective electrode is formed as thesecond electrode 302. Therefore, a single-layer structure or astacked-layer structure can be formed using one or more kinds of desiredelectrode materials. Note that the second electrode 302 is formed withthe use of a material selected as described above after the EL layer 303b is formed. These electrodes can be formed by a sputtering method or avacuum evaporation method.

<First Electrode and Second Electrode>

For materials used for the first electrode 301 and the second electrode302, any of the materials below can be used in an appropriatecombination as long as the functions of the electrodes described abovecan be fulfilled. For example, a metal, an alloy, an electricallyconductive compound, a mixture of these, and the like can beappropriately used. Specifically, an In—Sn oxide (also referred to asITO), an In—Si—Sn oxide (also referred to as ITSO), an In—Zn oxide, anIn—W—Zn oxide, or the like can be used. In addition, it is possible touse a metal such as aluminum (Al), titanium (Ti), chromium (Cr),manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu),gallium (Ga), zinc (Zn), indium (In), tin (Sn), molybdenum (Mo),tantalum (Ta), tungsten (W), palladium (Pd), gold (Au), platinum (Pt),silver (Ag), yttrium (Y), or neodymium (Nd) or an alloy containing anappropriate combination of any of these metals. It is also possible touse a Group 1 element or a Group 2 element in the periodic table, whichis not described above (e.g., lithium (Li), cesium (Cs), calcium (Ca),or strontium (Sr)), a rare earth metal such as europium (Eu) orytterbium (Yb), an alloy containing an appropriate combination of any ofthese elements, graphene, or the like.

In the light-emitting element in FIG. 3D, when the first electrode 301is an anode, a hole-injection layer 311 a and a hole-transport layer 312a of the EL layer 303 a are sequentially stacked over the firstelectrode 301 by a vacuum evaporation method. After the EL layer 303 aand the charge generation layer 304 are formed, a hole-injection layer311 b and a hole-transport layer 312 b of the EL layer 303 b aresequentially stacked over the charge generation layer 304 in a similarmanner.

<Hole-Injection Layer and Hole-Transport Layer>

The hole-injection layers (311 a and 311 b) inject holes from the firstelectrode 301 that is an anode to the EL layers (303 a and 303 b) andeach contain a material with a high hole-injection property.

As examples of the material with a high hole-injection property,transition metal oxides such as molybdenum oxide, vanadium oxide,ruthenium oxide, tungsten oxide, and manganese oxide can be given.Alternatively, it is possible to use any of the following materials:phthalocyanine-based compounds such as phthalocyanine (abbreviation:H₂Pc) and copper phthalocyanine (abbreviation: CuPc); aromatic aminecompounds such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB) andN,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD); high molecular compounds such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)(abbreviation: PEDOT/PSS); and the like.

Alternatively, as the material with a high hole-injection property, acomposite material containing a hole-transport material and an acceptormaterial (an electron-accepting material) can also be used. In thatcase, the acceptor material extracts electrons from a hole-transportmaterial, so that holes are generated in the hole-injection layer 311,and the holes are injected into the light-emitting layers (313 a and 313b) through the hole-transport layers (312 a and 312 b). Note that eachof the hole-injection layers (311 a and 311 b) may be formed to have asingle-layer structure using a composite material containing ahole-transport material and an acceptor material (an electron-acceptingmaterial), or a stacked-layer structure in which a layer including ahole-transport material and a layer including an acceptor material (anelectron-accepting material) are stacked.

The hole-transport layers (312 a and 312 b) transport the holes, whichare injected from the first electrode 301 by the hole-injection layers(311 a and 311 b), to the light-emitting layers (313 a and 313 b). Notethat the hole-transport layers (312 a and 312 b) each contain ahole-transport material. It is particularly preferable that the HOMOlevel of the hole-transport material included in the hole-transportlayers (312 a and 312 b) be the same as or close to that of thehole-injection layers (311 a and 311 b).

Examples of the acceptor material used for the hole-injection layers(311 a and 311 b) include an oxide of a metal belonging to any of Group4 to Group 8 of the periodic table. Specifically, molybdenum oxide,vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, tungstenoxide, manganese oxide, and rhenium oxide can be given. Among these,molybdenum oxide is especially preferable since it is stable in the airand its hygroscopic property is low and is easily treated.Alternatively, organic acceptors such as a quinodimethane derivative, achloranil derivative, and a hexaazatriphenylene derivative can be used.Specifically, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane(abbreviation: F₄-TCNQ), chloranil,2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation:HAT-CN), or the like can be used.

The hole-transport materials used for the hole-injection layers (311 aand 311 b) and the hole-transport layers (312 a and 312 b) arepreferably materials with a hole mobility of more than or equal to 10⁻⁶cm²/Vs. Note that other materials may be used as long as the materialshave a hole-transport property higher than an electron-transportproperty.

Preferred hole-transport materials are π-electron rich heteroaromaticcompounds (e.g., carbazole derivatives and indole derivatives) andaromatic amine compounds, examples of which include compounds having anaromatic amine skeleton, such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD),4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine(abbreviation: mBPAFLP),4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP), 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole(abbreviation: PCPPn),N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-amine(abbreviation: PCBiF),

N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF),4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBBi1BP),4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBANB),4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBNBB),9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine(abbreviation: PCBAF),N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine(abbreviation: PCBASF), 4,4′,4″-tris(carbazol-9-yl)triphenylamine(abbreviation: TCTA), 4,4′,4″-tris(N,N′-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB); compounds having a carbazole skeleton, such as1,3-bis(N-carbazolyl)benzene (abbreviation: mCP),4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP),3,3′-bis(9-phenyl-9H-carbazole) (abbreviation: PCCP),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene(abbreviation: TCPB), and9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation: CzPA);compounds having a thiophene skeleton, such as4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II),2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene(abbreviation: DBTFLP-III), and4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene(abbreviation: DBTFLP-IV); and compounds having a furan skeleton, suchas 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation:DBF3P-II) and4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran(abbreviation: mmDBFFLBi-II).

A high molecular compound such as poly(N-vinylcarbazole) (abbreviation:PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation:PTPDMA), or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine](abbreviation: Poly-TPD) can also be used.

Note that the hole-transport material is not limited to the aboveexamples and one of or a combination of various known materials may beused as the hole-transport material for the hole-injection layers (311 aand 311 b) and the hole-transport layers (312 a and 312 b).

Next, in the light-emitting element in FIG. 3D, the light-emitting layer313 a is formed over the hole-transport layer 312 a of the EL layer 303a by a vacuum evaporation method. After the EL layer 303 a and thecharge generation layer 304 are formed, the light-emitting layer 313 bis formed over the hole-transport layer 312 b of the EL layer 303 b by avacuum evaporation method.

<Light-Emitting Layer>

The light-emitting layers (313 a and 313 b) each contain alight-emitting material. Note that as the light-emitting material, amaterial whose light emission color is blue, violet, bluish violet,green, yellowish green, yellow, orange, red, or the like isappropriately used. When the plurality of light-emitting layers (313 aand 313 b) are formed using different light-emitting materials,different light emission colors can be exhibited (for example,complementary light emission colors are combined to achieve white lightemission). Furthermore, a stacked-layer structure in which onelight-emitting layer contains two or more kinds of light-emittingmaterials may be employed.

The light-emitting layers (313 a and 313 b) each may contain one or morekinds of organic compounds (a host material and an assist material) inaddition to a light-emitting material (a guest material). As the one ormore kinds of organic compounds, one or both of the hole-transportmaterial and the electron-transport material described in thisembodiment can be used.

In one embodiment of the present invention, it is preferable that alight-emitting material which emits blue light (a blue-light-emittingmaterial) be used as a guest material in one of the light-emittinglayers (313 a and 313 b) in the light-emitting element and a materialwhich emits green light (a green-light-emitting material) and a materialwhich emits red light (a red-light-emitting material) be used in theother light-emitting layer. This manner is effective in the case wherethe blue-light-emitting material (the blue-light-emitting layer) has alower light emission efficiency or a shorter lifetime than the materials(layers) which emit other colors. Here, it is preferable that alight-emitting material that converts singlet excitation energy intoemission of light in the visible light range be used as theblue-light-emitting material and light-emitting materials that converttriplet excitation energy into emission of light in the visible lightrange be used as the green- and red-light-emitting materials, wherebythe spectrum balance between R, G, and B is improved.

There is no particular limitation on the light-emitting materials thatcan be used for the light-emitting layers (313 a and 313 b), and alight-emitting material that converts singlet excitation energy intoemission of light in the visible light range or a light-emittingmaterial that converts triplet excitation energy into emission of lightin the visible light range can be used. Examples of the light-emittingmaterial are given below.

As an example of the light-emitting material that converts singletexcitation energy into light emission, a material emitting fluorescence(a fluorescent material) can be given. Examples of the material emittingfluorescence include a pyrene derivative, an anthracene derivative, atriphenylene derivative, a fluorene derivative, a carbazole derivative,a dibenzothiophene derivative, a dibenzofuran derivative, adibenzoquinoxaline derivative, a quinoxaline derivative, a pyridinederivative, a pyrimidine derivative, a phenanthrene derivative, and anaphthalene derivative. A pyrene derivative is particularly preferablebecause it has a high light emission quantum yield. Specific examples ofthe pyrene derivative includeN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPm),N,N′-diphenyl-N,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine(abbreviation: 1,6FLPAPm),N,N′-bis(dibenzofuran-2-yl)-N,N′-diphenylpyrene-1,6-diamine(abbreviation: 1,6FrAPrn),N,N′-bis(dibenzothiophen-2-yl)-N,N′-diphenylpyrene-1,6-diamine(abbreviation: 1,6ThAPm),N,N′-(pyrene-1,6-diyl)bis[(N-phenylbenzo[b]naphtho[1,2-d]furan)-6-amine](abbreviation:1,6BnfAPrn),N,N′-(pyrene-1,6-diyl)bis[(N-phenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation: 1,6BnfAPm-02), andN,N′-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation: 1,6BnfAPm-03). In addition, the pyrene derivative is agroup of compounds effective for meeting the chromaticity of blue (thechromaticity range represented by the region C) in one embodiment of thepresent invention.

In addition, it is possible to use5,6-bis[4-(10-phenyl-9-anthryl)phenyl]-2,2′-bipyridine (abbreviation:PAP2BPy), 5,6-bis[4′-(10-phenyl-9-anthryl)biphenyl-4-yl]-2,2′-bipyridine(abbreviation: PAPP2BPy),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),4-[4-(10-phenyl-9-anthryl)phenyl]-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPBA), perylene, 2,5,8,11-tetra(tert-butyl)perylene(abbreviation: TBP),N,N′-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA), or the like.

As examples of a light-emitting material that converts tripletexcitation energy into light emission, a material emittingphosphorescence (a phosphorescent material) and a thermally activateddelayed fluorescence (TADF) material that exhibits thermally activateddelayed fluorescence can be given.

Examples of a phosphorescent material include an organometallic complex,a metal complex (a platinum complex), and a rare earth metal complex.These materials exhibit the respective light emission colors (lightemission peaks) and thus, any of them is appropriately selectedaccording to need.

As examples of a phosphorescent material which emits blue or green lightand whose light emission spectrum has a peak wavelength of greater thanor equal to 450 nm and less than or equal to 570 nm, the followingmaterials can be given.

For example, organometallic complexes having a 4H-triazole skeleton,such astris{2-[5-(2-methylphenyl)-4-(2,6-dimethylphenyl)-4H-1,2,4-triazol-3-yl-κN2]phenyl-κC}iridium(III)(abbreviation: [Ir(mpptz-dmp)₃]),tris(5-methyl-3,4-diphenyl-4H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Mptz)₃]),tris[4-(3-biphenyl)-5-isopropyl-3-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(iPrptz-3b)₃]), andtris[3-(5-biphenyl)-5-isopropyl-4-phenyl-4H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(iPr5btz)₃]); organometallic complexes having a1H-triazole skeleton, such astris[3-methyl-1-(2-methylphenyl)-5-phenyl-1H-1,2,4-triazolato]iridium(III)(abbreviation: [Ir(Mptz1-mp)₃]) andtris(1-methyl-5-phenyl-3-propyl-1H-1,2,4-triazolato)iridium(III)(abbreviation: [Ir(Prptz1-Me)₃]); organometallic complexes having animidazole skeleton, such asfac-tris[1-(2,6-diisopropylphenyl)-2-phenyl-1H-imidazole]iridium(III)(abbreviation: [Ir(iPrpmi)₃]) andtris[3-(2,6-dimethylphenyl)-7-methylimidazo[1,2-f]phenanthridinato]iridium(III)(abbreviation: [Ir(dmpimpt-Me)₃]); organometallic complexes in which aphenylpyridine derivative having an electron-withdrawing group is aligand, such asbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic), bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: [Ir(CF₃ppy)₂(pic)]),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)); and the like can be given.

As examples of a phosphorescent material which emits green or yellowlight and whose light emission spectrum has a peak wavelength of greaterthan or equal to 495 nm and less than or equal to 590 nm, the followingmaterials can be given.

For example, organometallic iridium complexes having a pyrimidineskeleton, such as tris(4-methyl-6-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₃]),tris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(tBuppm)₃]),(acetylacetonato)bis(6-methyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(mppm)₂(acac)]),(acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III)(abbreviation: [Ir(tBuppm)₂(acac)]),(acetylacetonato)bis[6-(2-norbornyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(nbppm)₂(acac)]),(acetylacetonato)bis[5-methyl-6-(2-methylphenyl)-4-phenylpyrimidinato]iridium(III)(abbreviation: [Ir(mpmppm)₂(acac)]), (acetylacetonato)bis{4,6-dimethyl-2-[6-(2,6-dimethylphenyl)-4-pyrimidinyl-N3]phenyl-κC}iridium(III)(abbreviation: [Ir(dmppm-dmp)₂(acac)]), and(acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III)(abbreviation: [Ir(dppm)₂(acac)]); organometallic iridium complexeshaving a pyrazine skeleton, such as(acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-Me)₂(acac)]) and(acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-iPr)₂(acac)]); organometallic iridium complexeshaving a pyridine skeleton, such as tris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: [Ir(ppy)₃]),bis(2-phenylpyridinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: [Ir(ppy)₂(acac)]), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: [Ir(bzq)₂(acac)]),tris(benzo[h]quinolinato)iridium(III) (abbreviation: [Ir(bzq)₃]),tris(2-phenylquinolinato-N, C^(2′))iridium(III) (abbreviation:[Ir(pq)₃]), and bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(pq)₂(acac)]); organometalliccomplexes such as bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(dpo)₂(acac)]),bis{2-[4′-(perfluorophenyl)phenyl]pyridinato-N,C^(2′)}iridium(III)acetylacetonate (abbreviation: [Ir(p-PF-ph)₂(acac)]), andbis(2-phenylbenzothiazolato-N, C^(2′))iridium(III) acetylacetonate(abbreviation: [Ir(bt)₂(acac)]); and rare earth metal complexes such astris(acetylacetonato) (monophenanthroline)terbium(III) (abbreviation:[Tb(acac)₃(Phen)]) can be given.

Among the above, an organometallic complex having a pyridine skeleton(particularly, a phenylpyridine skeleton) or a pyrimidine skeleton is agroup of compounds effective for meeting the chromaticity of green (thechromaticity range represented by the region B) in one embodiment of thepresent invention.

As examples of a phosphorescent material which emits yellow or red lightand whose emission spectrum has a peak wavelength of greater than orequal to 570 nm and less than or equal to 750 nm, the followingmaterials can be given.

For example, organometallic complexes having a pyrimidine skeleton, suchas(diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III)(abbreviation: [Ir(5mdppm)₂(dibm)]),bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III)(abbreviation: [Ir(5mdppm)₂(dpm)]), andbis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: [Ir(d1npm)₂(dpm)]);organometallic complexes having a pyrazine skeleton, such as(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr)₂(dpm)]), bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-P)₂(dibm)]),bis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}(2,2,6,6-tetramethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-dmCP)₂(dpm)]),(acetylacetonato)bis[2-methyl-3-phenylquinoxalinato-N,C^(2′)]iridium(III)(abbreviation: [Ir(mpq)₂(acac)]),(acetylacetonato)bis(2,3-diphenylquinoxalinato-N,C^(2′))iridium(III)(abbreviation: [Ir(dpq)₂(acac)]), and(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: [Ir(Fdpq)₂(acac)]); organometallic complexes having apyridine skeleton, such astris(1-phenylisoquinolinato-N,C^(2′))iridium(III) (abbreviation:[Ir(piq)₃]) and bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate (abbreviation: [Ir(piq)₂(acac)]); platinum complexessuch as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II)(abbreviation: [PtOEP]); and rare earth metal complexes such astris(1,3-diphenyl-1,3-propanedionato) (monophenanthroline)europium(III)(abbreviation: [Eu(DBM)₃(Phen)]) andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: [Eu(TTA)₃(Phen)]) can be given.

Among the above, an organometallic complex having a pyrazine skeleton isa group of compounds effective for meeting the chromaticity of red (thechromaticity range represented by the region A) in one embodiment of thepresent invention. In particular, an organometallic complex containing acyano group (e.g., [Ir(dmdppr-dmCP)₂(dpm)]) is preferable because it isstable.

Note that as the blue-light-emitting material, a material whosephotoluminescence peak wavelength is greater than or equal to 430 nm andless than or equal to 470 nm, preferably greater than or equal to 430 nmand less than or equal to 460 nm may be used. As thegreen-light-emitting material, a material whose photoluminescence peakwavelength is greater than or equal to 500 nm and less than or equal to540 nm, preferably greater than or equal to 500 nm and less than orequal to 530 nm may be used. As the red-light-emitting material, amaterial whose photoluminescence peak wavelength is greater than orequal to 610 nm and less than or equal to 680 nm, preferably greaterthan or equal to 620 nm and less than or equal to 680 nm may be used.Note that the photoluminescence may be measured with either a solutionor a thin film.

With the parallel use of such compounds and microcavity effect, theabove chromaticity can be more easily met. Here, a semi-transmissive andsemi-reflective electrode (a metal thin film portion) that is needed forobtaining microcavity effect preferably has a thickness of more than orequal to 20 nm and less than or equal to 40 nm, further preferably morethan 25 nm and less than or equal to 40 nm. However, the thickness ofmore than 40 nm possibly reduces the efficiency.

As the organic compounds (the host material and the assist material)used in the light-emitting layers (313 a and 313 b), one or more kindsof materials having a larger energy gap than the light-emitting material(the guest material) are used.

When the light-emitting material is a fluorescent material, it ispreferable to use an organic compound that has a high energy level in asinglet excited state and has a low energy level in a triplet excitedstate. For example, an anthracene derivative or a tetracene derivativeis preferably used. Specific examples include9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), 3-[4-(1-naphthyl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPN), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c, g]carbazole(abbreviation: cgDBCzPA),6-[3-(9,10-diphenyl-2-anthryl)phenyl]-benzo[b]naphtho[1,2-d]furan(abbreviation: 2mBnfPPA),9-phenyl-10-{4-(9-phenyl-9H-fluoren-9-yl)biphenyl-4′-yl}anthracene(abbreviation: FLPPA), 5,12-diphenyltetracene, and5,12-bis(biphenyl-2-yl)tetracene.

In the case where the light-emitting material is a phosphorescentmaterial, an organic compound having triplet excitation energy (energydifference between a ground state and a triplet excited state) which ishigher than that of the light-emitting material is preferably selected.In that case, it is possible to use a zinc- or aluminum-based metalcomplex, an oxadiazole derivative, a triazole derivative, abenzimidazole derivative, a quinoxaline derivative, a dibenzoquinoxalinederivative, a dibenzothiophene derivative, a dibenzofuran derivative, apyrimidine derivative, a triazine derivative, a pyridine derivative, abipyridine derivative, a phenanthroline derivative, an aromatic amine, acarbazole derivative, and the like.

Specific examples include metal complexes such astris(8-quinolinolato)aluminum(III) (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato) (4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP),2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBphen), and 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole(abbreviation: CO11); and aromatic amine compounds such as NPB, TPD, andBSPB.

In addition, condensed polycyclic aromatic compounds such as anthracenederivatives, phenanthrene derivatives, pyrene derivatives, chrysenederivatives, and dibenzo[g,p]chrysene derivatives can be used.Specifically, 9,10-diphenylanthracene (abbreviation: DPAnth),N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA), YGAPA, PCAPA,N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA), 2PCAPA, 6,12-dimethoxy-5,11-diphenylchrysene,DBC1, 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (abbreviation:CzPA), 3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),1,3,5-tri(1-pyrenyl)benzene (abbreviation: TPB3), or the like can beused.

In the case where a plurality of organic compounds are used for thelight-emitting layers (313 a and 313 b), it is preferable to usecompounds that form an exciplex in combination with each other. In thatcase, although any of various organic compounds can be combinedappropriately to be used, to form an exciplex efficiently, it isparticularly preferable to combine a compound that easily accepts holes(a hole-transport material) and a compound that easily accepts electrons(an electron-transport material). As the hole-transport material and theelectron-transport material, specifically, any of the materialsdescribed in this embodiment can be used.

Note that the TADF material is a material that can up-convert a tripletexcited state into a singlet excited state (i.e., reverse intersystemcrossing is possible) using a little thermal energy and efficientlyexhibits light emission (fluorescence) from the singlet excited state.The TADF is efficiently obtained under the condition where thedifference in energy between the triplet excitation level and thesinglet excitation level is greater than or equal to 0 eV and less thanor equal to 0.2 eV, preferably greater than or equal to 0 eV and lessthan or equal to 0.1 eV. Note that “delayed fluorescence” exhibited bythe TADF material refers to light emission having the same spectrum asnormal fluorescence and an extremely long lifetime. The lifetime is 10⁻⁶seconds or longer, preferably 10⁻³ seconds or longer.

Examples of the TADF material are fullerene, a derivative thereof, anacridine derivative such as proflavine, eosin, and the like. Otherexamples include a metal-containing porphyrin, such as a porphyrincontaining magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum(Pt), indium (In), or palladium (Pd). Examples of the metal-containingporphyrin include a protoporphyrin-tin fluoride complex (SnF₂(ProtoIX)), a mesoporphyrin-tin fluoride complex (SnF₂(Meso IX)), ahematoporphyrin-tin fluoride complex (SnF₂(Hemato IX)), a coproporphyrintetramethyl ester-tin fluoride complex (SnF₂(Copro III-4Me)), anoctaethylporphyrin-tin fluoride complex (SnF₂(OEP)), anetioporphyrin-tin fluoride complex (SnF₂(Etio I)), and anoctaethylporphyrin-platinum chloride complex (PtCl₂OEP).

Alternatively, a heterocyclic compound having a π-electron richheteroaromatic ring and a π-electron deficient heteroaromatic ring, suchas2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine(PIC-TRZ),2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine(PCCzPTzn),2-[4-(10H-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine(PXZ-TRZ),3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole(PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (ACRXTN),bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS), or10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (ACRSA) can beused. Note that a substance in which the π-electron rich heteroaromaticring is directly bonded to the π-electron deficient heteroaromatic ringis particularly preferable because both the donor property of theπ-electron rich heteroaromatic ring and the acceptor property of theπ-electron deficient heteroaromatic ring are increased and the energydifference between the singlet excited state and the triplet excitedstate becomes small.

Note that a TADF material can also be used in combination with anotherorganic compound.

Next, in the light-emitting element in FIG. 3D, the electron-transportlayer 314 a is formed over the light-emitting layer 313 a of the ELlayer 303 a by a vacuum evaporation method. After the EL layer 303 a andthe charge generation layer 304 are formed, the electron-transport layer314 b is formed over the light-emitting layer 313 b of the EL layer 303b by a vacuum evaporation method.

<Electron-Transport Layer>

The electron-transport layers (314 a and 314 b) transport the electrons,which are injected from the second electrode 302 by theelectron-injection layers (315 a and 315 b), to the light-emittinglayers (313 a and 313 b). Note that the electron-transport layers (314 aand 314 b) each contain an electron-transport material. It is preferablethat the electron-transport materials included in the electron-transportlayers (314 a and 314 b) be materials with an electron mobility ofhigher than or equal to 1×10⁻⁶ cm²/Vs. Note that other materials mayalso be used as long as the materials have an electron-transportproperty higher than a hole-transport property.

Examples of the electron-transport material include metal complexeshaving a quinoline ligand, a benzoquinoline ligand, an oxazole ligand,and a thiazole ligand; an oxadiazole derivative; a triazole derivative;a phenanthroline derivative; a pyridine derivative; and a bipyridinederivative. In addition, a π-electron deficient heteroaromatic compoundsuch as a nitrogen-containing heteroaromatic compound can also be used.

Specifically, it is possible to use metal complexes such as Alq₃,tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), BAlq,Zn(BOX)₂, and bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation:Zn(BTZ)₂), heteroaromatic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4′-tert-butylphenyl)-4-phenyl-5-(4″-biphenyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: Bphen),bathocuproine (abbreviation: BCP), and4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs), andquinoxaline derivatives and dibenzoquinoxaline derivatives such as2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:2mDBTPDBq-II),2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II),2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline(abbreviation: 2CzPDBq-III),7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:7mDBTPDBq-II), and6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation:6mDBTPDBq-II).

Further alternatively, a high molecular compound such aspoly(2,5-pyridinediyl) (abbreviation: PPy),poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)](abbreviation: PF-Py) orpoly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](abbreviation: PF-BPy) can be used.

Each of the electron-transport layers (314 a and 314 b) is not limitedto a single layer, but may be a stack of two or more layers eachcontaining any of the above materials.

Next, in the light-emitting element in FIG. 3D, the electron-injectionlayer 315 a is formed over the electron-transport layer 314 a of the ELlayer 303 a by a vacuum evaporation method. Subsequently, the EL layer303 a and the charge generation layer 304 are formed, the components upto the electron-transport layer 314 b of the EL layer 303 b are formedand then, the electron-injection layer 315 b is formed thereover by avacuum evaporation method.

<Electron-Injection Layer>

The electron-injection layers (315 a and 315 b) each contain a materialhaving a high electron-injection property. The electron-injection layers(315 a and 315 b) can each be formed using an alkali metal, an alkalineearth metal, or a compound thereof, such as lithium fluoride (LiF),cesium fluoride (CsF), calcium fluoride (CaF₂), or lithium oxide (LiOx).A rare earth metal compound like erbium fluoride (ErF₃) can also beused. Electride may also be used for the electron-injection layers (315a and 315 b). Examples of the electrode include a material in whichelectrons are added at high concentration to calcium oxide-aluminumoxide. Any of the materials for forming the electron-transport layers(314 a and 314 b), which are given above, can also be used.

A composite material in which an organic compound and an electron donor(donor) are mixed may also be used for the electron-injection layers(315 a and 315 b). Such a composite material is excellent in anelectron-injection property and an electron-transport property becauseelectrons are generated in the organic compound by the electron donor.The organic compound here is preferably a material excellent intransporting the generated electrons; specifically, for example, theelectron-transport materials for forming the electron-transport layers(314 a and 314 b) (e.g., a metal complex or a heteroaromatic compound)can be used. As the electron donor, a material showing anelectron-donating property with respect to the organic compound may beused. Preferable examples are an alkali metal, an alkaline earth metal,and a rare earth metal. Specifically, lithium, cesium, magnesium,calcium, erbium, ytterbium, and the like can be given. Furthermore, analkali metal oxide and an alkaline earth metal oxide are preferable, anda lithium oxide, a calcium oxide, a barium oxide, and the like can begiven. Alternatively, Lewis base such as magnesium oxide can be used.Further alternatively, an organic compound such as tetrathiafulvalene(abbreviation: TTF) can be used.

In the case where light obtained from the light-emitting layer 313 b isamplified, for example, the optical path length between the secondelectrode 302 and the light-emitting layer 313 b is preferably less thanone fourth of the wavelength λ of light emitted by the light-emittinglayer 313 b. In that case, the optical path length can be adjusted bychanging the thickness of the electron-transport layer 314 b or theelectron-injection layer 315 b.

<Charge Generation Layer>

The charge generation layer 304 has a function of injecting electronsinto the EL layer 303 a and injecting holes into the EL layer 303 b whena voltage is applied between the first electrode (anode) 301 and thesecond electrode (cathode) 302. The charge generation layer 304 may haveeither a structure in which an electron acceptor (acceptor) is added toa hole-transport material or a structure in which an electron donor(donor) is added to an electron-transport material. Alternatively, bothof these structures may be stacked. Note that by formation of the chargegeneration layer 304 with the use of any of the above materials, it ispossible to suppress the increase in drive voltage caused when the ELlayers are stacked.

In the case where the charge generation layer 304 has a structure inwhich an electron acceptor is added to a hole-transport material, any ofthe materials described in this embodiment can be used as thehole-transport material. As the electron acceptor, it is possible to use7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like. In addition, an oxide of metals thatbelong to Group 4 to Group 8 of the periodic table can be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, rhenium oxide,or the like is used.

In the case where the charge generation layer 304 has a structure inwhich an electron donor is added to an electron-transport material, anyof the materials described in this embodiment can be used as theelectron-transport material. As the electron donor, it is possible touse an alkali metal, an alkaline earth metal, a rare earth metal, metalsthat belong to Groups 2 and 13 of the periodic table, or an oxide orcarbonate thereof. Specifically, lithium (Li), cesium (Cs), magnesium(Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesiumcarbonate, or the like is preferably used. Alternatively, an organiccompound such as tetrathianaphthacene may be used as the electron donor.

<Substrate>

The light-emitting element described in this embodiment can be formedover a variety of substrates. Note that the type of the substrate is notlimited to a certain type. Examples of the substrate include asemiconductor substrate (e.g., a single crystal substrate or a siliconsubstrate), an SOI substrate, a glass substrate, a quartz substrate, aplastic substrate, a metal substrate, a stainless steel substrate, asubstrate including stainless steel foil, a tungsten substrate, asubstrate including tungsten foil, a flexible substrate, an attachmentfilm, paper including a fibrous material, and a base material film.

Examples of the glass substrate include a barium borosilicate glasssubstrate, an aluminoborosilicate glass substrate, and a soda lime glasssubstrate. Examples of a flexible substrate, an attachment film, and abase material film include plastics typified by polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), and polyethersulfone (PES); a synthetic resin such as acrylic; polypropylene;polyester; polyvinyl fluoride; polyvinyl chloride; polyamide; polyimide;aramid; epoxy; an inorganic vapor deposition film; and paper.

For formation of the light-emitting element in this embodiment, a vacuumprocess such as an evaporation method or a solution process such as aspin coating method or an ink-jet method can be used. When anevaporation method is used, a physical vapor deposition method (PVDmethod) such as a sputtering method, an ion plating method, an ion beamevaporation method, a molecular beam evaporation method, or a vacuumevaporation method, a chemical vapor deposition method (CVD method), orthe like can be used. Specifically, the functional layers (thehole-injection layers (311 a and 311 b), the hole-transport layers (312a and 312 b), the light-emitting layers (313 a and 313 b), theelectron-transport layers (314 a and 314 b), the electron-injectionlayers (315 a and 315 b)) included in the EL layers and the chargegeneration layer 304 of the light-emitting element can be formed by anevaporation method (e.g., a vacuum evaporation method), a coating method(e.g., a dip coating method, a die coating method, a bar coating method,a spin coating method, or a spray coating method), a printing method(e.g., an ink-jet method, screen printing (stencil), offset printing(planography), flexography (relief printing), gravure printing, ormicro-contact printing), or the like.

Note that materials that can be used for the functional layers (thehole-injection layers (311 a and 311 b), the hole-transport layers (312a and 312 b), the light-emitting layers (313 a and 313 b), theelectron-transport layers (314 a and 314 b), and the electron-injectionlayers (315 a and 315 b)) that are included in the EL layers (303 a and303 b) and the charge generation layer 304 in the light-emitting elementdescribed in this embodiment are not limited to the above materials, andother materials can be used in combination as long as the functions ofthe layers are fulfilled. For example, a high molecular compound (e.g.,an oligomer, a dendrimer, or a polymer), a middle molecular compound (acompound between a low molecular compound and a high molecular compoundwith a molecular weight of 400 to 4000), an inorganic compound (e.g., aquantum dot material), or the like can be used. The quantum dot may be acolloidal quantum dot, an alloyed quantum dot, a core-shell quantum dot,a core quantum dot, or the like.

The structure described in this embodiment can be used in an appropriatecombination with any of the structures described in the otherembodiments.

Embodiment 3

In this embodiment, a display device of one embodiment of the presentinvention which has a first element layer including a liquid crystalelement and a second element layer including a light-emitting elementand in which the display elements can perform the respective kinds ofdisplay is described. Note that such a display device can also bereferred to as an emission and reflection hybrid display or anemission/reflection hybrid display (ER-hybrid display) or the like.

The display device in this embodiment, which can perform both displayusing the liquid crystal element and display using the light-emittingelement, can be driven with extremely low power consumption in theoutdoors and other bright places where ambient light is intense when areflective liquid crystal element is used as the liquid crystal elementbecause the display can be performed with the reflective liquid crystalelement utilizing the ambient light. In the case where the ambient lightis too intense resulting in surface reflection, images can be displayedwith the use of both the liquid crystal element and the light-emittingelement at the same time. On the other hand, the display device canperform image display with a wide viewing angle and a high colorreproducibility and can be driven with low power consumption in thenighttime or in the indoors and other dark places where ambient light isweak when the light-emitting element, which does not need a lightsource, is used. Alternatively, a structure can be employed in which atransmissive (or a semi-transmissive and semi-reflective electrode)liquid crystal element is used as the liquid crystal element and thelight-emitting element is used as both the light source of the liquidcrystal element and a display element. Thus, a combination of the liquidcrystal element and the light-emitting element can display images withhigh color reproducibility at low power consumption as compared toconventional display panels.

The display device in FIG. 4A has a structure in which a first elementlayer (display element layer) 410 including a reflective liquid crystalelement 401, a second element layer (display element layer) 411including a light-emitting element 402, a third element layer (drivingelement layer) 412 including transistors (425 and 426) which drive theseelements (the liquid crystal element 401 and the light-emitting element402) are stacked. In FIG. 4A, the third element layer (driving elementlayer) 412 is positioned between the first element layer (displayelement layer) 410 and the second element layer (display element layer)411. However, the present invention is not limited thereto. When thestructure in FIG. 4A is simplified and illustrated like the structure inFIG. 4B, the display device can have the stacked layer structures inFIGS. 4C to 4E as the other variations.

In each of the display devices in FIGS. 4A to 4E, the liquid crystalelement 401 included in the first element layer (display element layer)410 and the light-emitting element 402 included in the second elementlayer (display element layer) 411 can be driven in the following modes:display is performed with the liquid crystal element 401 by reflectionof visible light on the conductive layer 403 serving as a firstelectrode (reflective electrode) in a first mode; and display isperformed by emission of light from the light-emitting element 402through an opening 404 in the conductive layer 403 in a second mode, forexample.

Note that the first element layer 410 including the liquid crystalelement 401, the second element layer 411 including the light-emittingelement 402, and the third element layer 412 including the transistors(driving elements) (425 and 426) can be stacked by a technique in whichthe layers are formed separately, peeled, and bonded to each other. Notethat in the case where the stacked-layer structure is formed by bondingin the above manner, the element layers are stacked with insulatinglayers provided therebetween. The elements (the liquid crystal element401, the light-emitting element 402, the transistors (425 and 426), andthe like) formed in the element layers can be electrically connected viaconductive films (wirings) formed in the insulating layers that insulatethe elements from one another.

The liquid crystal element 401 included in the first element layer 410is a reflective liquid crystal element. The conductive layer 403 servesas a reflective electrode, and is thus formed using a material with highreflectivity. Note that the conductive layer 403 includes the opening404. Furthermore, a conductive layer 407 serves as a transparentelectrode, and is thus formed using a material that transmits visiblelight. The conductive layer 403 and the conductive layer 407 are incontact with each other and function as one electrode of the liquidcrystal element 401. A conductive layer 408 functions as the otherelectrode of the liquid crystal element 401. Alignment films 415 and 416are provided on the conductive layers 407 and 408, respectively and incontact with the liquid crystal layer 409. An insulating layer 419formed in contact with a color filter 418 serves as an overcoat. Notethat the alignment films 415 and 416 are not necessarily provided whennot needed.

In addition, it is preferable that a spacer which has a function ofpreventing the electrodes of the liquid crystal element 401 from beingtoo close to each other (a function of keeping a cell gap) be provided,though not illustrated here.

The light-emitting element 402 included in the second element layer 411has a stacked-layer structure in which an EL layer 422 is providedbetween a conductive layer 420 serving as one electrode and a conductivelayer 421 serving as the other electrode. Note that the conductive layer421 includes a material transmitting visible light and the conductivelayer 420 includes a material reflecting visible light. Thus, lightemitted from the light-emitting element 402 which is transmitted throughthe conductive layer 420 is emitted to the outside of the substrate 405such that the light is transmitted through a color filter 423,transmitted through the liquid crystal element 401 via the opening 404,and then transmitted through a polarizing layer 424.

One of a source and a drain of the transistor 426, which is one of thetransistors (425 and 426) included in the third element layer 412, iselectrically connected to the conductive layer 403 and the conductivelayer 407 of the liquid crystal element 401 through a terminal portion427. Note that the transistor 426 corresponds to a transistor SW1 inFIG. 6 that will be described later. One of a source and a drain of thetransistor 425 is electrically connected to the conductive layer 420 inthe light-emitting element 402. For example, the transistor 425corresponds to a transistor M in FIG. 6.

Note that the transistors (425 and 426) are electrically connected tothe outside via an FPC or the like, though not illustrated here.

FIG. 5A is a block diagram illustrating a display device. A displaydevice includes a circuit (G) 501, a circuit (S) 502, and a displayportion 503. In the display portion 503, a plurality of pixels 504 arearranged in an R direction and a C direction in a matrix. A plurality ofwirings G1, wirings G2, wirings ANO, and wirings CSCOM are electricallyconnected to the circuit (G) 501. These wirings are also electricallyconnected to the plurality of pixels 504 arranged in the R direction. Aplurality of wirings S1 and wirings S2 are electrically connected to thecircuit (S) 502, and these wirings are also electrically connected tothe plurality of pixels 504 arranged in the C direction.

Each of the plurality of pixels 504 includes a liquid crystal elementand a light-emitting element. The liquid crystal element and thelight-emitting element include portions overlapping with each other.

FIG. 5B1 shows the shape of a conductive film 505 serving as areflective electrode of the liquid crystal element included in the pixel504. Note that an opening 507 is provided in a position 506 which ispart of the conductive film 505 and which overlaps with thelight-emitting element. That is, light emitted from the light-emittingelement is emitted through the opening 507.

The pixels 504 in FIG. 5B1 are arranged such that the pixels 504adjacent in the R direction exhibit different colors. Furthermore, theopenings 507 are provided so as not to be arranged in a line in the Rdirection. Such arrangement has an effect of suppressing crosstalkbetween the light-emitting elements of adjacent pixels 504. Furthermore,there is an advantage that element formation is facilitated.

The opening 507 can have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, a cross shape, a stripe shape, or aslit-like shape, for example.

FIG. 5B2 illustrates another example of the arrangement of theconductive films 505.

The ratio of the opening 507 to the total area of the conductive film505 (excluding the opening 507) affects the display of the displaydevice. That is, a problem is caused in that as the area of the opening507 is larger, the display using the liquid crystal element becomesdarker; in contrast, as the area of the opening 507 is smaller, thedisplay using the light-emitting element becomes darker. Furthermore, inaddition to the problem of the ratio of the opening, a small area of theopening 507 itself also causes a problem in that extraction efficiencyof light emitted from the light-emitting element is decreased. The ratioof the opening 507 to the total area of the conductive film 505(excluding the opening 507) is preferably 5% or more and 60% or lessbecause the visibility can be maintained even when the liquid crystalelement and the light-emitting element are used in a combination.

Next, an example of a circuit configuration of the pixel 504 isdescribed with reference to FIG. 6. FIG. 6 illustrates two adjacentpixels 504.

The pixel 504 includes the transistor SW1, a capacitor C1, a liquidcrystal element 510, a transistor SW2, the transistor M, a capacitor C2,a light-emitting element 511, and the like. Note that these componentsare electrically connected to any of the wiring G1, the wiring G2, thewiring ANO, the wiring CSCOM, the wiring S1, and the wiring S2 in thepixel 504. The liquid crystal element 510 and the light-emitting element511 are electrically connected to a wiring VCOM1 and a wiring VCOM2,respectively.

A gate of the transistor SW1 is connected to the wiring G1. One of asource and a drain of the transistor SW1 is connected to the wiring Si,and the other of the source and the drain is connected to one electrodeof the capacitor C1 and one electrode of the liquid crystal element 510.The other electrode of the capacitor C1 is electrically connected to thewiring CSCOM. The other electrode of the liquid crystal element 510 isconnected to the wiring VCOM1.

A gate of the transistor SW2 is connected to the wiring G2. One of asource and a drain of the transistor SW2 is connected to the wiring S2,and the other of the source and the drain is connected to one electrodeof the capacitor C2 and a gate of the transistor M. The other electrodeof the capacitor C2 is connected to one of a source and a drain of thetransistor M and the wiring ANO. The other of the source and the drainof the transistor M is connected to one electrode of the light-emittingelement 511. Furthermore, the other electrode of the light-emittingelement 511 is connected to the wiring VCOM2.

Note that the transistor M includes two gates between which asemiconductor is provided and which are electrically connected to eachother. With such a structure, the amount of current flowing through thetransistor M can be increased.

The on/off state of the transistor SW1 is controlled by a signal fromthe wiring G1. A predetermined potential is applied from the wiringVCOM1. Furthermore, orientation of liquid crystals of the liquid crystalelement 510 can be controlled by a signal from the wiring Si. Apredetermined potential is applied from the wiring CSCOM.

The on/off state of the transistor SW2 is controlled by a signal fromthe wiring G2. By the difference between the potentials applied from thewiring VCOM2 and the wiring ANO, the light-emitting element 511 can emitlight. Furthermore, the conduction state of the transistor M iscontrolled by a signal from the wiring S2.

In the above structure, in the case of the first mode, for example, theliquid crystal element 510 is controlled by the signals applied from thewiring G1 and the wiring S1 and optical modulation is utilized, wherebydisplay can be performed. In the case of the second mode, thelight-emitting element 511 emits light when the signals are applied fromthe wiring G2 and the wiring S2, whereby display can be performed. Inthe case where both modes are performed at the same time, desireddisplay can be performed by the liquid crystal element 510 and thelight-emitting element 511 on the basis of the signals from the wiringG1, the wiring G2, the wiring Si, and the wiring S2.

Note that the structure described in this embodiment can be used in anappropriate combination with any of the structures described in theother embodiments.

Embodiment 4

In this embodiment, an example of the transistor formed in the drivingelement layer included in the element layer of the display device of oneembodiment of the present invention is described. As the transistor, forexample, a planar transistor, a staggered transistor, an invertedstaggered transistor, or the like can be used. A top-gate or bottom-gatetransistor structure can be employed. Gate electrodes may be providedabove and below a channel. Thus, there are no particular limitations onthe structure of any of the transistors.

As a semiconductor material used for the semiconductor layer of thetransistor, an element of Group 14 (e.g., silicon or germanium), acompound semiconductor, or an oxide semiconductor can be used, forexample. A semiconductor containing silicon, a semiconductor containinggallium arsenide, an oxide semiconductor containing indium, or the likecan be typically used.

There is no particular limitation on the crystallinity of asemiconductor material used for the semiconductor layer of thetransistor, and an amorphous semiconductor or a semiconductor havingcrystallinity (a microcrystalline semiconductor, a polycrystallinesemiconductor, a single crystal semiconductor, or a semiconductor partlyincluding crystal regions) may be used. A semiconductor havingcrystallinity is preferably used, in which case deterioration of thetransistor characteristics can be suppressed.

Among the above semiconductor materials used for the semiconductor layerof the transistor, it is particularly preferable to use a metal oxide.

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into oxideinsulators, oxide conductors (including transparent oxide conductors),oxide semiconductors (also simply referred to as OS), and the like. Forexample, a metal oxide used in an active layer of a transistor is calledan oxide semiconductor in some cases. In other words, an OS FET can meana transistor including a metal oxide or an oxide semiconductor.

In this specification and the like, a metal oxide including nitrogen isalso called a metal oxide in some cases. Moreover, a metal oxideincluding nitrogen may be called a metal oxynitride.

Next, an oxide semiconductor which is a metal oxide will be described.

An oxide semiconductor is a semiconductor material having a wider bandgap and a lower carrier density than silicon and thus can reduce theoff-state current of a transistor. It is particularly preferable to usean oxide semiconductor having an energy gap of 2 eV or more, furtherpreferably 2.5 eV or more, and still further preferably 3 eV or more.

When a transistor has a reduced off-state current, charge accumulated ina capacitor that is connected in series to the transistor can be heldfor a long time. Accordingly, when such a transistor is used for apixel, operation of a driver circuit can be stopped while a gray scaleof an image displayed in each display region is maintained. As a result,a display device with extremely low power consumption can be obtained.

In this specification and the like, “c-axis aligned crystal (CAAC)” or“cloud-aligned composite (CAC)” may be stated. CAAC refers to an exampleof a crystal structure, and CAC refers to an example of a function or amaterial composition.

In this specification and the like, CAC-OS or CAC-metal oxide has afunction of a conductor in a part of the material and has a function ofa dielectric (or insulator) in another part of the material; as a whole,CAC-OS or CAC-metal oxide has a function of a semiconductor. In the casewhere CAC-OS or CAC-metal oxide is used in an active layer of atransistor, the conductor has a function of letting electrons (or holes)serving as carriers flow, and the dielectric has a function of notletting electrons serving as carriers flow. By the complementary actionof the function as a conductor and the function as a dielectric, CAC-OSor CAC-metal oxide can have a switching function (on/off function). Inthe CAC-OS or CAC-metal oxide, separation of the functions can maximizeeach function.

In this specification and the like, CAC-OS or CAC-metal oxide includesconductor regions and dielectric regions. The conductor regions have theabove-described function of the conductor, and the dielectric regionshave the above-described function of the dielectric. In some cases, theconductor regions and the dielectric regions in the material areseparated at the nanoparticle level. In some cases, the conductorregions and the dielectric regions are unevenly distributed in thematerial. The conductor regions are observed to be coupled in acloud-like manner with their boundaries blurred, in some cases.

In other words, CAC-OS or CAC-metal oxide can be called a matrixcomposite or a metal matrix composite.

Furthermore, in the CAC-OS or CAC-metal oxide, the conductor regions andthe dielectric regions each have a size of more than or equal to 0.5 nmand less than or equal to 10 nm, preferably more than or equal to 0.5 nmand less than or equal to 3 nm and are dispersed in the material, insome cases.

Next, the above-mentioned CAC-OS will be described in detail.

The CAC-OS has, for example, a composition in which elements included inan oxide semiconductor are unevenly distributed. Materials includingunevenly distributed elements each have a size of greater than or equalto 0.5 nm and less than or equal to 10 nm, preferably greater than orequal to 1 nm and less than or equal to 2 nm, or a similar size. Notethat in the following description of an oxide semiconductor, a state inwhich one or more elements are unevenly distributed and regionsincluding the element(s) are mixed is referred to as a mosaic pattern ora patch-like pattern. The region has a size of greater than or equal to0.5 nm and less than or equal to 10 nm, preferably greater than or equalto 1 nm and less than or equal to 2 nm, or a similar size.

Note that an oxide semiconductor preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, anelement M (one or more kinds of elements selected from aluminum,gallium, yttrium, copper, vanadium, beryllium, boron, silicon, titanium,iron, nickel, germanium, zirconium, molybdenum, lanthanum, cerium,neodymium, hafnium, tantalum, tungsten, magnesium, and the like) may becontained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) hasa composition in which materials are separated into indium oxide(InO_(X1), where X1 is a real number greater than 0) or indium zincoxide (In_(X2)Zn_(Y2)O_(Z2), where X2, Y2, and Z2 are real numbersgreater than 0), and gallium oxide (GaO_(X3), where X3 is a real numbergreater than 0), gallium zinc oxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4, Y4,and Z4 are real numbers greater than 0), or the like, and a mosaicpattern is formed. Then, InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) forming themosaic pattern is evenly distributed in the film. This composition isalso referred to as a cloud-like composition.

That is, the CAC-OS is a composite oxide semiconductor with acomposition in which a region including GaO_(X3) as a main component anda region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main componentare mixed. Note that in this specification, for example, when the atomicratio of In to an element M in a first region is greater than the atomicratio of In to an element M in a second region, the first region hashigher In concentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1), (m1 is a natural number) and a crystalline compoundrepresented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≦x0≦1; m0 is agiven number).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanocrystals have c-axis alignment and are connected in the a-b planedirection without alignment.

On the other hand, the CAC-OS relates to the material composition of anoxide semiconductor. In a material composition of a CAC-OS including In,Ga, Zn, and O, nanoparticle regions including Ga as a main component areobserved in part of the CAC-OS and nanoparticle regions including In asa main component are observed in part thereof. These nanoparticleregions are randomly dispersed to form a mosaic pattern. Therefore, thecrystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure including two or morefilms with different atomic ratios is not included. For example, atwo-layer structure of a film including In as a main component and afilm including Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, yttrium, copper, vanadium,beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like are contained instead of gallium in a CAC-OS,nanoparticle regions including the selected metal element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionsincluding In as a main component are observed in part thereof, and thesenanoparticle regions are randomly dispersed to form a mosaic pattern inthe CAC-OS.

The CAC-OS can be formed by a sputtering method under conditions where asubstrate is intentionally not heated, for example. In the case offorming the CAC-OS by a sputtering method, one or more selected from aninert gas (typically, argon), an oxygen gas, and a nitrogen gas may beused as a deposition gas. The ratio of the flow rate of an oxygen gas tothe total flow rate of the deposition gas at the time of deposition ispreferably as low as possible, and for example, the flow ratio of anoxygen gas is preferably higher than or equal to 0% and less than 30%,further preferably higher than or equal to 0% and less than or equal to10%.

The CAC-OS is characterized in that no clear peak is observed inmeasurement using θ/2θ scan by an out-of-plane method, which is an X-raydiffraction (XRD) measurement method. That is, X-ray diffraction showsno alignment in the a-b plane direction and the c-axis direction in ameasured region.

In an electron diffraction pattern of the CAC-OS which is obtained byirradiation with an electron beam with a probe diameter of 1 nm (alsoreferred to as a nanometer-sized electron beam), a ring-like region withhigh luminance and a plurality of bright spots in the ring-like regionare observed. Therefore, the electron diffraction pattern indicates thatthe crystal structure of the CAC-OS includes a nanocrystal (nc)structure with no alignment in plan-view and cross-sectional directions.

For example, energy dispersive X-ray spectroscopy (EDX) is used toobtain EDX mapping, and according to the EDX mapping, the CAC-OS of theIn—Ga—Zn oxide has a composition in which the regions including GaO_(X3)as a main component and the regions including In_(X2)Zn_(Y2)O_(Z2) orInO_(X1) as a main component are unevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound inwhich metal elements are evenly distributed, and has characteristicsdifferent from those of the IGZO compound. That is, in the CAC-OS,regions including GaO_(X3) or the like as a main component and regionsincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component areseparated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component is higher than that of a region including GaO_(X3)or the like as a main component. In other words, when carriers flowthrough regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent, the conductivity of an oxide semiconductor is exhibited.Accordingly, when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) asa main component are distributed in an oxide semiconductor like a cloud,high field-effect mobility (t) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) orthe like as a main component is higher than that of a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when regions including GaO_(X3) or the like as a main component aredistributed in an oxide semiconductor, leakage current can be suppressedand favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor layer of atransistor, the insulating property derived from GaO_(X3) or the likeand the conductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)complement each other, whereby high on-state current (Ion) and highfield-effect mobility (pt) can be achieved.

When a CAC-OS is used for a semiconductor layer of a transistor, thetransistor can have increased reliability.

It is preferable that the atomic ratio of metal elements of a sputteringtarget used for depositing the In-M-Zn-based oxide satisfy In≧M andZn≧M. As the atomic ratio of metal elements of such a sputtering target,In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=4:2:4.1 and thelike are preferable. Note that the atomic ratio of metal elements in theformed film varies from the atomic ratio of those in the above-describedsputtering target, within a range of ±40%.

The formed film preferably has a low carrier density. An oxidesemiconductor with a low carrier density has a low impurityconcentration and a low density of defect states and can be regarded asan oxide semiconductor with stable characteristics. For example, for anoxide semiconductor film with a low carrier density, it is desirable touse an oxide semiconductor whose carrier density is lower than or equalto 1×10¹⁷/cm³, preferably lower than or equal to 1×10¹⁵/cm³, furtherpreferably lower than or equal to 1×10¹³/cm³, still further preferablylower than or equal to 1×10¹¹/cm³, even further preferably lower than1×10¹⁰/cm³, and higher than or equal to 1×10⁻⁹/cm³.

Note that without limitation to the compositions and materials describedabove, a material with an appropriate composition can be used dependingon required semiconductor characteristics and electrical characteristics(e.g., field-effect mobility and threshold voltage) of a transistor. Toobtain the required semiconductor characteristics of the transistor, itis preferable that the carrier density, the impurity concentration, thedefect density, the atomic ratio between a metal element and oxygen, theinteratomic distance, the density, and the like of the semiconductorlayer be set to appropriate values.

Alkali metal and alkaline earth metal might generate carriers whenbonded to an oxide semiconductor, in which case the off-state current ofthe transistor might be increased. Therefore, the concentration ofalkali metal or alkaline earth metal of the semiconductor layer, whichis measured by secondary ion mass spectrometry, is lower than or equalto 1×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁶ atoms/cm³.

When an oxide semiconductor is used, the crystal structure thereof maybe a non-single-crystal structure. Examples of the non-single-crystalstructure include the above-described CAAC-OS, a polycrystallinestructure, a microcrystalline structure, and an amorphous structure.Among the non-single-crystal structures, the amorphous structure has thehighest density of defect states, whereas a CAAC-OS has the lowestdensity of defect states. The amorphous structure has disordered atomicarrangement or an absolutely amorphous structure and no crystal portion.

Note that the semiconductor layer may be a mixed film including two ormore of the following: a region having an amorphous structure, a regionhaving a microcrystalline structure, a region having a polycrystallinestructure, a region of CAAC-OS, and a region having a single-crystalstructure. The mixed film has, for example, a single-layer structure ora stacked-layer structure including two or more of the above regions insome cases.

When a transistor in the driving element layer included in the elementlayer of the display device of one embodiment of the present inventionis the transistor described in this embodiment, the display device canhave high reliability.

Note that the structure described in this embodiment can be used in anappropriate combination with any of the structures described in theother embodiments.

Embodiment 5

In this embodiment, examples of a variety of electronic devices and anautomobile manufactured using a display device of one embodiment of thepresent invention are described.

Examples of the electronic device including the display device aretelevision devices (also referred to as TV or television receivers),monitors for computers and the like, digital cameras, digital videocameras, digital photo frames, mobile phones (also referred to ascellular phones or portable telephone devices), portable game consoles,goggle-type displays (e.g., VR goggles), mobile information terminals,audio playback devices, large game machines such as pachinko machines,and the like. Specific examples of these electronic devices areillustrated in FIGS. 7A, 7B, 7C, 7D, 7D′-1, 7D′-2, and 7E, and FIGS. 8Ato 8C.

FIG. 7A illustrates an example of a television device. In a televisiondevice 7100, a display portion 7103 is incorporated in a housing 7101.The display portion 7103 can display images and may be a touch panel (aninput/output device) including a touch sensor (an input device). Notethat the display device of one embodiment of the present invention canbe used for the display portion 7103. In addition, here, the housing7101 is supported by a stand 7105.

The television device 7100 can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can be changedand images displayed on the display portion 7103 can be controlled.Furthermore, the remote controller 7110 may be provided with a displayportion 7107 for displaying data output from the remote controller 7110.

Note that the television device 7100 is provided with a receiver, amodem, and the like. With the use of the receiver, general televisionbroadcasts can be received. Moreover, when the television device isconnected to a communication network with or without wires via themodem, one-way (from a sender to a receiver) or two-way (between asender and a receiver or between receivers) information communicationcan be performed.

FIG. 7B illustrates a computer, which includes a main body 7201, ahousing 7202, a display portion 7203, a keyboard 7204, an externalconnection port 7205, a pointing device 7206, and the like. Note thatthis computer can be manufactured using the display device of oneembodiment of the present invention for the display portion 7203. Thedisplay portion 7203 may be a touch panel (an input/output device)including a touch sensor (an input device). Note that the computer canbe especially suitable for outdoor use by including the display deviceof one embodiment of the present invention because a reduction invisibility due to reflection of ambient light can be prevented in thedisplay device.

FIG. 7C illustrates a smart watch, which includes a housing 7302, adisplay portion 7304, operation buttons 7311 and 7312, a connectionterminal 7313, a band 7321, a clasp 7322, and the like.

The display portion 7304 mounted in the housing 7302 serving as a bezelincludes a non-rectangular display region. The display portion 7304 candisplay an icon 7305 indicating time, another icon 7306, and the like.The display portion 7304 may be a touch panel (an input/output device)including a touch sensor (an input device). Note that the smart watchcan be especially suitable for outdoor use by including the displaydevice of one embodiment of the present invention because a reduction invisibility due to reflection of ambient light can be prevented in thedisplay device.

The smart watch illustrated in FIG. 7C can have a variety of functions,such as a function of displaying a variety of information (e.g., a stillimage, a moving image, and a text image) on a display portion, a touchpanel function, a function of displaying a calendar, date, time, and thelike, a function of controlling processing with a variety of software(programs), a wireless communication function, a function of beingconnected to a variety of computer networks with a wirelesscommunication function, a function of transmitting and receiving avariety of data with a wireless communication function, and a functionof reading program or data stored in a recording medium and displayingthe program or data on a display portion.

The housing 7302 can include a speaker, a sensor (a sensor having afunction of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone, and the like. Note that the smart watch can be manufacturedusing the display device for the display portion 7304.

FIG. 7D illustrates an example of a mobile phone (e.g., a smartphone). Amobile phone 7400 includes a housing 7401 provided with a displayportion 7402, a microphone 7406, a speaker 7405, a camera 7407, anexternal connection portion 7404, an operation button 7403, and thelike. In the case where a display device is manufactured in the mannerthat the liquid crystal element and light-emitting element of oneembodiment of the present invention are formed over a flexiblesubstrate, the display device can be used for the display portion 7402having a curved surface as illustrated in FIG. 7D.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 7D is touched with a finger or the like, data can be input into themobile phone 7400. Furthermore, operations such as making a call andcomposing an e-mail can be performed by touch on the display portion7402 with a finger or the like.

The display portion 7402 has mainly three screen modes. The first modeis a display mode mainly for displaying images. The second mode is aninput mode mainly for inputting data such as text. The third mode is adisplay-and-input mode in which two modes of the display mode and theinput mode are combined.

For example, in the case of making a call or composing an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 and text input operation can be performed using charactersdisplayed on the screen. In this case, it is preferable to display akeyboard or number buttons on almost the entire screen of the displayportion 7402.

When a detection device such as a gyroscope sensor or an accelerationsensor is provided inside the mobile phone 7400, display on the screenof the display portion 7402 can be automatically changed by determiningthe orientation of the mobile phone 7400 (whether the mobile phone isplaced horizontally or vertically).

The screen modes are changed by touch on the display portion 7402 oroperation with the operation button 7403 of the housing 7401.Alternatively, the screen modes can be switched depending on kinds ofimages displayed on the display portion 7402. For example, when a signalof an image displayed on the display portion is a signal of moving imagedata, the screen mode is switched to the display mode. When the signalis a signal of text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed within a specified period while a signal detectedby an optical sensor in the display portion 7402 is detected, the screenmode may be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may also function as an image sensor. Forexample, an image of a palm print, a fingerprint, or the like is takenby touch on the display portion 7402 with the palm or the finger,whereby personal authentication can be performed. In addition, when abacklight or a sensing light source that emits near-infrared light isprovided in the display portion, an image of a finger vein, a palm vein,or the like can be taken. Note that the mobile phone can be especiallysuitable for outdoor use by including the display device of oneembodiment of the present invention in the display portion 7402 becausea reduction in visibility due to reflection of ambient light can beprevented in the display device.

Furthermore, the display device can be used for a mobile phone having astructure illustrated in FIG. 7D′-1 or FIG. 7D′-2, which is anotherstructure of the mobile phone (e.g., smartphone).

Note that in the case of the structure illustrated in FIG. 7D′-1 or FIG.7D′-2, text data, image data, or the like can be displayed on secondscreens 7502(1) and 7502(2) of housings 7500(1) and 7500(2) as well asfirst screens 7501(1) and 7501(2). Such a structure enables the user toeasily see text data, image data, or the like displayed on the secondscreens 7502(1) and 7502(2) while the mobile phone is placed in user'sbreast pocket.

FIG. 7E shows a goggle-type display (a head-mounted display), whichincludes a main body 7601, a display portion 7602, and an arm 7603. Notethat the goggle-type display can be especially suitable for outdoor useby including the display device of one embodiment of the presentinvention in the display portion 7602 because a reduction in visibilitydue to reflection of ambient light can be prevented.

Another electronic device including the display device is a foldablemobile information terminal illustrated in FIGS. 8A to 8C. FIG. 8Aillustrates a mobile information terminal 9310 which is opened. FIG. 8Billustrates the mobile information terminal 9310 which is being openedor being folded. FIG. 8C illustrates the mobile information terminal9310 which is folded. The mobile information terminal 9310 is highlyportable when folded and is highly browsable when opened because of aseamless large display region.

A display portion 9311 is supported by three housings 9315 joinedtogether by hinges 9313. Note that the display portion 9311 may be atouch panel (an input/output device) including a touch sensor (an inputdevice). When the display portion 9311 is bent at a connection portionbetween two housings 9315 with the use of the hinges 9313, the mobileinformation terminal 9310 can be reversibly changed in shape from anopened state to a folded state. A display region 9312 in the displayportion 9311 is a display region that is positioned at a side surface ofthe mobile information terminal 9310 that is folded. On the displayregion 9312, information icons, file shortcuts of frequently usedapplications or programs, and the like can be displayed, andconfirmation of information and start of application can be smoothlyperformed. Note that the mobile information terminal can be especiallysuitable for outdoor use by including the display device of oneembodiment of the present invention in the display portion 9311 becausea reduction in visibility due to reflection of ambient light can beprevented in the display device.

FIGS. 9A and 9B illustrate an automobile including the display device.The display device can be incorporated in the automobile, andspecifically, can be included in lights 5101 (including lights of therear part of the car), a wheel 5102 of a tire, a part or whole of a door5103, or the like on the outer side of the automobile which isillustrated in FIG. 9A. The display device can also be included in adisplay portion 5104, a steering wheel 5105, a gear lever 5106, a seat5107, an inner rearview mirror 5108, or the like on the inner side ofthe automobile which is illustrated in FIG. 9B, or in a part of a glasswindow. Note that the display device of one embodiment the presentinvention which is provided in part of the automobile can be especiallysuitable for outdoor use because a reduction in visibility due toreflection of ambient light from the display device can be prevented.

As described above, the electronic devices and automobiles can beobtained using the display device of one embodiment of the presentinvention. Note that the display device can be used for electronicdevices and automobiles in a variety of fields without being limited tothe electronic devices and automobiles described in this embodiment.

Note that the structure described in this embodiment can be used in anappropriate combination with any of the structures described in theother embodiments.

Example 1

Simulations were performed to examine the relation between thebrightness (reflectance) and the NTSC coverage in a display including areflective liquid crystal element (a reflective display) and the resultsare described in this example.

The light source of a reflective display is ambient light, and it isdifficult to adjust the luminance of the light source as appropriate.The outside light is transmitted twice through a color filter whenentering a display and exiting from the display; thus, it can be saidthat the reflectivity is largely affected by the color filter. That is,the reflectivity can be controlled as the thickness of the color filteris adjusted.

Then, the reflectivity of a display was changed as the thickness of thecolor filter was adjusted, and the relation between the reflectance andthe NTSC coverage was estimated by liquid crystal alignment simulation.For the calculation, LCD Master 1D manufactured by SHINTECH, Inc. wasused. The calculation conditions are shown in Table 1 below. Note thatthe incident light was set to 100% on the assumption that thereflectance was specular reflection.

TABLE 1 Algorithm 2x2 (Single reflection) Light source D65 Polar angle 0 LC mode Twisted ECB LC ZLI-4792 Gap 2 μm Twist 70 Applied Voltage 0/6V

FIG. 10 shows the simulation results.

Next, the NTSC area ratio and the NTSC coverage as a function of thereflectance were measured using an actual reflective display. Themeasurement was performed in the manner that light was incident at apolar angle of 30° and received at 0°. Specular reflection is notemployed; thus, the reflectance of a standard white plate is set to100%. Note that the conditions of a reflective display panel used forthis measurement are shown in Table 2 below.

TABLE 2 LC mode Twisted ECB Pixel density 212 ppi Aperture ratio 83.4%Dn 0.100 De 3.56 Gap 2 μm Twist 70 Applied Voltage 0/6 V

FIG. 11 shows the measurement results.

Here, the simulation results in FIG. 10 and the measurement results(actual measurement results) in FIG. 11 were corrected so as to becomparable with each other because the reflectance in the simulation andthe reflectance in the measurement are differently defined.Specifically, the reflectance when the light source was 100% wasmultiplied by a constant such that a curve of the NTSC coverage withrespect to the reflectance obtained by simulation was fitted to theplots of the measurement results. FIG. 12 shows the results.

The results in FIG. 12 indicate that a reflectance of more than or equalto 16% and less than or equal to 26% can be obtained in the panelincluding a reflective liquid crystal element when the NTSC area ratioor the NTSC coverage is set to more than or equal to 20% and less thanor equal to 60%. That is, it is apparent that brightness (reflectance)required for the display including a reflective liquid crystal element(reflective display) can be obtained when the NTSC area ratio or theNTSC coverage is more than or equal to 20% and less than or equal to60%.

Example 2

In this example, an element structure, a forming method, and propertiesof a light-emitting element used in the display device of one embodimentof the present invention will be described. Note that FIG. 13illustrates an element structure of a light-emitting element describedin this example, and Table 3 shows specific structures. Table 3 alsoshows color filters (CF) combined with light-emitting elements. Alight-emitting element 1 is combined with a CF-R; a light-emittingelement 2, a CF-G; and each of light-emitting elements 3 and 4, a CF-B.FIG. 14 shows transmitting properties of these CFs. Chemical formulae ofmaterials used in this example are shown below.

TABLE 3 First hole- Light- First hole- transport emitting First Firstelectrode injection layer layer layer (A) electron-transport layerSymbol in FIG. 13 901 911a 912a 913a 914a Light-emitting Ag—Pd—Cu ITSOPCPPn:MoOx PCPPn *1 cgDBCzPA NBphen element 1(R) (200 nm) (110 nm)(1:0.5 10 nm) (10 nm) (10 nm) (15 nm) Light-emitting ITSO PCPPn:MoOxelement 2(G)  (45 nm) (1:0.5 20 nm) Light-emitting ITSO PCPPn:MoOxelement 3(B1)  (10 nm) (1:0.5 12.5 nm) Light-emitting ITSO PCPPn:MoOxelement 4(B1.5) (110 nm) (1:0.5 16 nm) First Light-emitting layer (B)electron- Charge Second hole- First light- Second injection generationSecond hole-injection transport emitting light-emitting layer layerlayer layer layer layer Symbol in FIG. 13 915a 904 911b 912b 913(b1)913(b2) (Reference) Light-emitting Li₂O CuPc DBT3P-II:MoOx BPAFLP *2 *3Light-emitting element 1(R) (0.1 nm) (2 nm) (1:0.5 10 nm) (15 nm)element 1(R) Light-emitting Light-emitting element 2(G) element 2(G)Light-emitting Llight-emitting element 3(B1) element 3(B1)Light-emitting Light-emitting element 4(B1.5) element 4(B1.5) SecondSecond electron-transport electron- layer injection layer Secondelectrode Symbol in FIG. 13 914b 915b 903 CF Light-emitting2mDBTBPDBq-II Nbphen LiF Ag:Mg ITO CF-R Light-emitting element 1(R) (25nm) (15 nm) (1 nm) (1:0.1 25 nm) (70 nm) element 1(R) Light-emittingCF-G Light-emitting element 2(G) element 2(G) Light-emitting CF-BLight-emitting element 3(B1) element 3(B1) Light-emitting CF-BLight-emitting element 4(B1.5) element 4(B1.5) *1 cgDBCzPA:1,6BnfAPrn-03(1:0.03 25 nm) *2 2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₃] (0.8:0.2:0.06 20nm) *3 2mDBTBPDBq-II:[Ir(dmdppr-P)₂(dibm)] (1:0.04 20 nm)

<<Formation of Light-Emitting Element>>

A light-emitting element in this example has a structure illustrated inFIG. 13 in which a first electrode 901 is formed over a substrate 900, afirst EL layer 902 a is formed over the first electrode 901, a chargegeneration layer 904 is formed over the first EL layer 902 a, a secondEL layer 902 b is formed over the charge generation layer 904, and asecond electrode 903 is formed over the second EL layer 902 b. Note thatthe light-emitting element 1 in this example is a light-emitting elementemitting mainly red light and referred to as a light-emitting element1(R). The light-emitting element 2 is a light-emitting element emittingmainly green light and referred to as a light-emitting element 2(G). Thelight-emitting element 3 and the light-emitting element 4 are each alight-emitting element emitting mainly blue light and are also referredto as a light-emitting element 3(B1) and a light-emitting element3(B1.5), respectively.

First, the first electrode 901 was formed over the substrate 900. Theelectrode area was set to 4 mm² (2 mm×2 mm). A glass substrate was usedas the substrate 900. The first electrode 901 was formed in thefollowing manner: a 200-nm-thick alloy film of silver (Ag), palladium(Pd), and copper (Cu) (the alloy is also referred to as Ag—Pd—Cu) wasformed by a sputtering method, and an ITSO was formed by a sputteringmethod. The ITSO was formed such that the thickness was 110 nm in thecase of the light-emitting element 1(R), the thickness was 45 nm in thecase of the light-emitting element 2(G), the thickness was 10 nm in thecase of the light-emitting element 3(B1), and the thickness was 110 nmin the case of the light-emitting element 4(B1.5). In this example, thefirst electrode 901 functions as an anode. The first electrode 901 is areflective electrode having a function of reflecting light. In thisexample, both the light-emitting element 3(B1) and the light-emittingelement 4(B1.5) emit blue light but have different optical path lengthsbetween their electrodes. The light-emitting element 3(B1) has anadjusted optical path length between its electrodes of 1 wavelength andthe light-emitting element 4(B1.5) has an adjusted optical path lengthbetween its electrodes of 1.5 wavelengths.

As pretreatment, a surface of the substrate was washed with water,baking was performed at 200° C. for one hour, and then UV ozonetreatment was performed for 370 seconds. After that, the substrate wastransferred into a vacuum evaporation apparatus where the pressure hadbeen reduced to approximately 10⁻⁴ Pa, and was subjected to vacuumbaking at 170° C. for 60 minutes in a heating chamber of the vacuumevaporation apparatus, and then the substrate was cooled down for about30 minutes.

Next, a first hole-injection layer 911 a was formed over the firstelectrode 901. After the pressure in the vacuum evaporation apparatuswas reduced to 10⁻⁴ Pa, the hole-injection layer 911 a was formed byco-evaporation such that the weight ratio of3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn)to molybdenum oxide was 1:0.5, and such that the thickness was 10 nm inthe case of the light-emitting element 1(R), the thickness was 20 nm inthe case of the light-emitting element 2(G), the thickness was 12.5 nmin the case of the light-emitting element 3(B1), and the thickness was16 nm in the case of the light-emitting element 4(B1.5).

Then, a first hole-transport layer 912 a was formed over the firsthole-injection layer 911 a. As the first hole-transport layer 912 a,PCPPn was deposited by evaporation to a thickness of 10 nm. Note thatthe same applies to the first light-emitting element, the secondlight-emitting element, the third light-emitting element, and the fourthlight-emitting element. When the same applies to all the light-emittingelements, there is no description hereinafter.

Next, a light-emitting layer (A) 913 a was formed over the firsthole-transport layer 912 a.

The light-emitting layer (A) 913 a was formed to a thickness of 25 nm byco-evaporation using7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) as a host material and usingN,N′-(pyrene-1,6-diyl)bis[(6,N-diphenylbenzo[b]naphtho[1,2-d]furan)-8-amine](abbreviation: 1,6BnfAPrn-03) as a guest material (a fluorescentmaterial), such that the weight ratio of cgDBCzPA to 1,6BnfAPrn-03 was1:0.03.

Next, a first electron-transport layer 914 a was formed over thelight-emitting layer (A) 913 a. The first electron-transport layer 914 awas formed in the following manner: cgDBCzPA and2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (abbreviation:NBphen) were sequentially deposited by evaporation to thicknesses of 10nm and 15 nm, respectively.

Next, a first electron-injection layer 915 a was formed over the firstelectron-transport layer 914 a. The first electron-injection layer 915 awas formed to a thickness of 0.1 nm by evaporation of lithium oxide(Li₂O).

Then, the charge generation layer 904 was formed over the firstelectron-injection layer 915 a. The charge generation layer 904 wasformed by evaporation of copper phthalocyanine (abbreviation: CuPc) to athickness of 2 nm.

Next, a second hole-injection layer 911 b was formed over the chargegeneration layer 904. The second hole-injection layer 911 b was formedto a thickness of 10 nm by co-evaporation such that the weight ratio of4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation:DBT3P-II) to molybdenum oxide was 1:0.5.

Then, a second hole-transport layer 912 b was formed over the secondhole-injection layer 911 b. The hole-transport layer 912 b was formed toa thickness of 15 nm by evaporation of4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP).

A light-emitting layer (B) 913 b was formed over the secondhole-transport layer 912 b. The light-emitting layer (B) 913 b had astacked-layer structure of a first light-emitting layer (B1) 913(b 1)and a second light-emitting layer (B2) 913(b 2).

The first light-emitting layer (B1) 913(b 1) was formed to a thicknessof 20 nm by co-evaporation using2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline(abbreviation: 2mDBTBPDBq-II) as a host material, usingN-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine(abbreviation: PCBBiF) as an assist material, and usingtris(4-t-butyl-6-phenylpyrimidinato)iridium(III) (abbreviation:[Ir(tBuppm)₃]) as a guest material (a phosphorescent material) such thatthe weight ratio of 2mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₃] was 0.8:0.2:0.06.The second light-emitting layer (B2) 913(b 2) was formed to a thicknessof 20 nm by co-evaporation using 2mDBTBPDBq-II as a host material andusing bis{4,6-dimethyl-2-[3-(3,5-dimethylphenyl)-5-phenyl-2-pyrazinyl-κN]phenyl-κC}(2,6-dimethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-P)₂(dibm)]) as a guest material (aphosphorescent material), such that the weight ratio of 2mDBTBPDBq-II to[Ir(dmdppr-P)₂(dibm)] was 1:0.04.

Next, a second electron-transport layer 914 b was formed over the secondlight-emitting layer (B2) 913(b 2). The second electron-transport layer914 b was formed in the following manner: 2mDBTBPDBq-II and NBphen weresequentially deposited by evaporation to thicknesses of 10 nm and 15 nm,respectively.

Then, a second electron-injection layer 915 b was formed over the secondelectron-transport layer 914 b. The second electron-injection layer 915b was formed to a thickness of 1 nm by evaporation of lithium fluoride(LiF).

Then, the second electrode 903 was formed over the secondelectron-injection layer 915 b. The second electrode 903 was formed inthe following manner: a film of silver (Ag) and magnesium (Mg) wasformed to a thickness of 15 nm by co-evaporation at a volume ratio ofAg:Mg=1:0.1, and then indium tin oxide (ITO) was formed to a thicknessof 70 nm by a sputtering method. In this example, the second electrode903 functions as a cathode. Moreover, the second electrode 903 is asemi-transmissive and semi-reflective electrode having functions oftransmitting light and reflecting light.

Through the above steps, the light-emitting element in which the ELlayers are provided between the pair of electrodes was formed over thesubstrate 900. The first hole-injection layer 911 a, the firsthole-transport layer 912 a, the light-emitting layer 913 a, the firstelectron-transport layer 914 a, the first electron-injection layer 915a, the second hole-injection layer 911 b, the second hole-transportlayer 912 b, the light-emitting layer (B) 913 b, the secondelectron-transport layer 914 b, and the second electron-injection layer915 b that are described above are functional layers forming the ELlayers of one embodiment of the present invention. Furthermore, in allthe evaporation steps in the above forming method, evaporation wasperformed by a resistance-heating method.

The light-emitting element formed in this example is sealed between thesubstrate 900 and a substrate 905 as illustrated in FIG. 13. Thesubstrate 905 is provided with a color filter 906. The sealing betweenthe substrate 900 and the substrate 905 was performed in such a mannerthat the substrate 905 was fixed to the substrate 900 with a sealingmaterial in a glove box containing a nitrogen atmosphere, a sealant wasapplied to surround the light-emitting element formed over the substrate900, and then irradiation with 365-nm ultraviolet light at 6 J/cm² wasperformed and heat treatment was performed at 80° C. for 1 hour forsealing.

The light-emitting elements formed in this example each have a structurein which light is emitted in the direction indicated by the arrow fromthe second electrode 903 side of the light-emitting element.

<<Operation Characteristics of Light-Emitting Elements>>

Operation characteristics of the formed light-emitting elements weremeasured. Note that the measurement was performed at room temperature(in an atmosphere kept at 25° C.). The results are shown in FIG. 15,FIG. 16, FIG. 17, and FIG. 18. FIG. 19 shows light emission spectra whencurrent at a current density of 2.5 mA/cm² was applied to thelight-emitting elements. The light emission spectra were measured with amulti-channel spectrometer (PMA-12 produced by Hamamatsu PhotonicsK.K.). As shown in FIG. 19, the light emission spectrum of thelight-emitting element 1(R) which emits red light has a peak around 635nm, the light emission spectrum of the light-emitting element 2(G) whichemits green light has a peak around 521 nm, and the light emissionspectra of the light-emitting elements 3(B1) and 4(B1.5) which emit bluelight each have a peak around 453 nm. The spectrum shapes were narrowed.In this example, the results of measuring light emission obtained from acombination of light-emitting elements and color filters are shown.

FIG. 14 shows transmission spectra of the color filter (red) (CF-R) usedin combination with the light-emitting element 1(R), the color filter(green) (CF-G) used in combination with the light-emitting element 2(G),and the color filter (blue) (CF-B) used in combination with thelight-emitting elements 3(B1) and 4(B1.5). FIG. 14 shows that thetransmittance of the CF-R at 600 nm is lower than or equal to 60% and is52%, whereas the transmittance of the CF-R at 650 nm is higher than orequal to 70% and is 89%. In addition, the transmittance of the CF-G at480 nm and at 580 nm are lower than or equal to 60% and are 26% and 52%,respectively, whereas the transmittance of the CF-G at 530 nm is higherthan or equal to 70% and is 72%. Furthermore, the transmittance of theCF-B at 510 nm is lower than or equal to 60% and is 60%, whereas thetransmittance of the CF-B at 450 nm is higher than or equal to 70% andis 80%.

The results of measuring the chromaticities (x, y) of the light-emittingelements formed in this example (the light-emitting element 1(R), thelight-emitting element 2(G), and the light-emitting element 3(B1)) witha luminance colorimeter (BM-5A manufactured by TOPCON CORPORATION) areshown in Table 4 below. The chromaticity of the light-emitting element1(R) was measured at a luminance of approximately 730 cd/m². Thechromaticity of the light-emitting element 2(G) was measured at aluminance of approximately 1800 cd/m². The chromaticity of thelight-emitting element 3(B1) was measured at a luminance ofapproximately 130 cd/m². Note that white light emission close to D65 canbe obtained by summing the luminance of R, the luminance of G, and theluminance of B.

TABLE 4 x y Light-emitting 0.697 0.297 element 1(R) Light-emitting 0.1860.778 element 2(G) Light-emitting 0.142 0.046 element 3(B1)

On the basis of the results in Table 4, the BT.2020 area ratio and theBT.2020 coverage were calculated using these chromaticities (x, y) andwere 93% and 91%, respectively. Note that the BT.2020 area ratio wasobtained in such a manner that an area A of a triangle formed byconnecting the CIE chromaticity coordinates (x, y) of RGB which fulfillthe BT.2020 standard and area B of a triangle formed by connecting theCIE chromaticity coordinates (x, y) of the three light-emitting elementsdescribed in this example were calculated and the area ratio (B/A) wascalculated. The BT.2020 coverage is a value which represents how muchpercentage of the BT.2020 standard color gamut (the inside of the abovetriangle) can be reproduced using a combination of the chromaticities ofthe three light-emitting elements described in this example.

The results of measuring the chromaticities (x, y) of the light-emittingelement 1(R), the light-emitting element 2(G), and the light-emittingelement 4(B1.5)) with a luminance colorimeter among the light-emittingelements formed in this example are shown in Table 5 below. Thechromaticity of the light-emitting element 1(R) was measured at aluminance of approximately 550 cd/m². The chromaticity of thelight-emitting element 2(G) was measured at a luminance of approximately1800 cd/m². The chromaticity of the light-emitting element 4(B1.5) wasmeasured at a luminance of approximately 130 cd/m². Note that whitelight emission close to D65 can be obtained by summing the luminance ofR, the luminance of G, and the luminance of B.

TABLE 5 x y Light-emitting 0.697 0.297 element 1(R) Light-emitting 0.1860.778 element 2(G) Light-emitting 0.156 0.042 element 4(B1.5)

On the basis of the results in Table 5, the BT.2020 area ratio and theBT.2020 coverage were calculated using the chromaticities (x, y) andwere 92% and 90%, respectively. Even such a structure having improvedblue light emission efficiency can achieve extremely wide-range colorreproducibility.

The above results shows that, in this example, the chromaticity of thelight-emitting element 1(R) falls within a chromaticity range in which xis more than 0.680 and less than or equal to 0.720 and y is more than orequal to 0.260 and less than or equal to 0.320, the chromaticity of thelight-emitting element 2(G) falls within a chromaticity range in which xis more than or equal to 0.130 and less than or equal to 0.250 and y ismore than 0.710 and less than or equal to 0.810, and the chromaticity ofthe light-emitting element 3(B1) falls within a chromaticity range inwhich x is more than or equal to 0.120 and less than or equal to 0.170and y is more than or equal to 0.020 and less than 0.060. Thelight-emitting element 1(R) has x of more than 0.680, and thusparticularly has a better red chromaticity than the Digital CinemaInitiatives (DCI-P3) standard, in which the chromaticity coordinates (x,y) of red (R) are (0.680, 0.320); green (G), (0.265, 0.690); and blue(B), (0.150, 0.060). The light-emitting element 2(G) has y of more than0.71, and thus particularly has a better green chromaticity than theDCI-P3 standard and the NTSC standard. In addition, the light-emittingelements 3(B1) and 4(B1.5) each have y of less than 0.06, and thusparticularly has a better blue chromaticity than the DCI-P3 standard.

Note that the chromaticities (x, y) of the light-emitting elements 1(R),2(G), 3(B1), and 4(B1.5) calculated using the values of the lightemission spectra shown in FIG. 19 are (0.693, 0.303), (0.202, 0.744),(0.139, 0.056), and (0.160, 0.057), respectively. Therefore, when thechromaticities of a combination of the light-emitting elements 1(R),2(G), and 3(B1) are calculated using the light emission spectra, theBT.2020 area ratio is 86% and the BT.2020 coverage is 84%. In addition,when the chromaticities of a combination of the light-emitting elements1(R), 2(G), and 4(B1.5) are calculated using the light emission spectra,the BT.2020 area ratio is 84% and the BT.2020 coverage is 82%.

Example 3

In this example, an element structure, a forming method, and propertiesof a light-emitting element used in a display device of one embodimentof the present invention will be described. Note that FIG. 13illustrates an element structure of a light-emitting element describedin this example, and Table 6 shows specific structures. Chemicalformulae of materials used in this example are shown below. The colorfilters whose transmission spectra are shown in FIG. 14 were used.

TABLE 6 First hole- Light- First hole- transport emitting First Firstelectrode injection layer layer layer (A) electron-transport layerSymbol in FIG. 13 901 911a 912a 913a 914a Light-emitting Ag—Pd—Cu ITSOPCPPn:MoOx PCPPn *1 cgDBCzPA NBphen element 5(R) (200 nm) (110 nm)(1:0.5 10 nm) (10 nm) (10 nm) (15 nm) Light-emitting ITSO PCPPn:MoOxelement 6(G)  (45 nm) (1:0.5 20 nm) Light-emitting ITSO PCPPn:MoOxelement 7(B1)  (10 nm) (1:0.5 12.5 nm) Light-emitting ITSO PCPPn:MoOxelement 8(B1.5) (110 nm) (1:0.5 19 nm) First Light-emitting layer (B)electron- Charge Second hole- First light- Second injection generationSecond hole-injection transport emitting light-emitting layer layerlayer layer layer layer Symbol in FIG. 13 915a 904 911b 912b 913(b1)913(b2) (Reference) Light-emitting Li₂O CuPc DBT3P-II:MoOx BPAFLP *2 *3Light-emitting element 5(R) (0.1 nm) (2 nm) (1:0.5 10 nm) (15 nm)element 5(R) Light-emitting Light-emitting element 6(G) element 6(G)Light-emitting Light-emitting element 7(B1) element 7(B1) Light-emittingLight-emitting element 8(B1.5) element 8(B1.5) Second Secondelectron-transport electron- layer injection layer Second electrodeSymbol in FIG. 13 914b 915b 903 CF Light-emitting 2mDBTBPDBq-II NbphenLiF Ag:Mg ITO CF-R Light-emitting element 5(R) (25 nm) (15 nm) (1 nm)(1:0.1 30 nm) (70 nm) element 5(R) Light-emitting CF-G Light-emittingelement 6(G) element 6(G) Light-emitting CF-B Light-emitting element7(B1) element 7(B1) Light-emitting CF-B Light-emitting element 8(B1.5)element 8(B1.5) *1 cgDBCzPA:1,6BnfAPrn-03 (1:0.03 25 nm) *22mDBTBPDBq-II:PCBBiF:[Ir(tBuppm)₃] (0.8:0.2:0.06 20 nm) *32mDBTBPDBq-II:[Ir(dmdppr-P)₂(dibm)] (1:0.04 20 nm)

<<Formation of Light-Emitting Element>>

A light-emitting element in this example has the structure illustratedin FIG. 13 in which the first electrode 901 is formed over the substrate900, the first EL layer 902 a is formed over the first electrode 901,the charge generation layer 904 is formed over the first EL layer 902 a,the second EL layer 902 b is formed over the charge generation layer904, and the second electrode 903 is formed over the second EL layer 902b as in Example 2. Note that a light-emitting element 5 in this exampleis a light-emitting element emitting mainly red light and referred to asa light-emitting element 5(R). A light-emitting element 6 is alight-emitting element emitting mainly green light and referred to as alight-emitting element 6(G). A light-emitting element 7 and alight-emitting element 8 are each a light-emitting element emittingmainly blue light and are also referred to as a light-emitting element7(B1) and a light-emitting element 8(B1.5), respectively.

In the light-emitting elements in this example, the thicknesses of thelayers formed at the time of forming the elements are different fromeach other. However, the layers can be formed using the same materialand in the same manner as in Example 2; therefore, Example 2 can bereferred to and description is omitted in this example.

<<Operation Characteristics of Light-Emitting Elements>>

Operation characteristics of the formed light-emitting elements weremeasured. Note that the measurement was performed at room temperature(in an atmosphere kept at 25° C.). The results are shown in FIG. 20,FIG. 21, FIG. 22, and FIG. 23. FIG. 24 shows light emission spectra whencurrent at a current density of 2.5 mA/cm² was applied to thelight-emitting elements. The light emission spectra were measured with amulti-channel spectrometer (PMA-12 produced by Hamamatsu PhotonicsK.K.). As shown in FIG. 24, the light emission spectrum of thelight-emitting element 5(R) which emits red light has a peak around 635nm, the light emission spectrum of the light-emitting element 6(G) whichemits green light has a peak around 530 nm, and the light emissionspectra of the light-emitting elements 7(B1) and 8(B1.5) which emit bluelight have peaks around 464 nm and 453 nm, respectively. The spectrumshapes were narrowed. In this example, the results of measuring lightemission obtained from a combination of light-emitting elements andcolor filters are shown.

Next, the results of measuring the chromaticities (x, y) of thelight-emitting elements formed in this example (the light-emittingelement 5(R), the light-emitting element 6(G), and the light-emittingelement 7(B1)) with a luminance colorimeter (BM-5A manufactured byTOPCON CORPORATION) are shown in Table 7 below. The chromaticity of thelight-emitting element 5(R) was measured at a luminance of approximately650 cd/m². The chromaticity of the light-emitting element 6(G) wasmeasured at a luminance of approximately 1900 cd/m². The chromaticity ofthe light-emitting element 7(B1) was measured at a luminance ofapproximately 140 cd/m². Note that white light emission close to D65 canbe obtained by summing the luminance of R, the luminance of G, and theluminance of B.

TABLE 7 x y Light-emitting 0.700 0.294 element 5(R) Light-emitting 0.1750.793 element 6(G) Light-emitting 0.142 0.039 element 7(B1)

On the basis of the results in Table 7, the BT.2020 area ratio and theBT.2020 coverage were calculated using the chromaticities (x, y) andwere 97% and 95%, respectively.

The results of measuring the chromaticities (x, y) of the light-emittingelement 5(R), the light-emitting element 6(G), and the light-emittingelement 8(B1.5)) among the light-emitting elements formed in thisexample with a luminance colorimeter are shown in Table 8 below. Thechromaticity of the light-emitting element 5(R) was measured at aluminance of approximately 650 cd/m². The chromaticity of thelight-emitting element 6(G) was measured at a luminance of approximately1900 cd/m². The chromaticity of the light-emitting element 8(B1.5) wasmeasured at a luminance of approximately 170 cd/m². Note that whitelight emission close to D65 can be obtained by summing the luminance ofR, the luminance of G, and the luminance of B.

TABLE 8 x y Light-emitting 0.700 0.294 element 5(R) Light-emitting 0.1750.793 element 6(G) Light-emitting 0.153 0.046 element 8(B1.5)

On the basis of the results in Table 8, the BT.2020 area ratio and theBT.2020 coverage were calculated using the chromaticities (x, y) andwere 95% and 93%, respectively. Even such a structure having improvedblue light emission efficiency can achieve extremely wide-range colorreproducibility.

The above results shows that, in this example, the chromaticity of thelight-emitting element 5(R) falls within a chromaticity range in which xis more than 0.680 and less than or equal to 0.720 and y is greater thanor equal to 0.260 and less than or equal to 0.320, the chromaticity ofthe light-emitting element 6(G) falls within a chromaticity range inwhich x is more than or equal to 0.130 and less than or equal to 0.250and y is more than 0.710 and less than or equal to 0.810, and thechromaticity of the light-emitting element 7(B1) falls within achromaticity range in which x is more than or equal to 0.120 and lessthan or equal to 0.170 and y is more than or equal to 0.020 and lessthan 0.060. The light-emitting element 6(G) has y of more than 0.71, andthus particularly has a better green chromaticity than the DCI-P3standard and the NTSC standard. In addition, the light-emitting elements7(B1) and 8(B1.5) each have y of less than 0.06, and thus particularlyhas a better blue chromaticity than the DCI-P3 standard.

Note that the chromaticities (x, y) of the light-emitting elements 5, 6,7, and 8 calculated using the values of the light emission spectra shownin FIG. 24 are (0.696, 0.300), (0.185, 0.760), (0.140, 0.048), and(0.154, 0.056), respectively. Therefore, when the chromaticities of acombination of the light-emitting elements 5(R), 6(G), and 7(B1) arecalculated using the light emission spectra, the BT.2020 area ratio is91% and the BT.2020 coverage is 89%. In addition, when thechromaticities of a combination of the light-emitting elements 5(R),6(G), and 8(B1.5) are calculated using the light emission spectra, theBT.2020 area ratio is 88% and the BT.2020 coverage is 86%.

Reference Example

In this reference example, a synthesis method of bis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-N]phenyl-κC}(2,2,6,6-tetramethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-dmCP)₂(dpm)]) (Structural formula (100)),which is an organometallic complex and a light-emitting material thatcan be used for the light-emitting layer in the light-emitting elementof one embodiment of the present invention, is described. Theorganometallic complex has a peak of a light emission spectrum at morethan or equal to 600 nm and less than or equal to 700 nm. The structureof [Ir(dmdppr-dmCP)₂(dpm)] is shown below.

Step 1: Synthesis of 5-hydroxy-2,3-(3,5-dimethylphenyl)pyrazine

First, 5.27 g of 3,3′,5,5′-tetramethylbenzyl, 2.61 g of glycinamidehydrochloride, 1.92 g of sodium hydroxide, and 50 mL of methanol wereput into a three-necked flask equipped with a reflux pipe, and the airin the flask was replaced with nitrogen. After that, the mixture wasstirred at 80° C. for 7 hours to cause a reaction. Then, 2.5 mL of 12Mhydrochloric acid was added thereto and stirring was performed for 30minutes. Then, 2.02 g of potassium bicarbonate was added, and stirringwas performed for 30 minutes. After the resulting suspension wassubjected to suction filtration, the obtained solid was washed withwater and methanol to give an objective pyrazine derivative as milkywhite powder in a yield of 79%. A synthesis scheme of Step 1 is shown in(a-1).

Step 2: Synthesis of 5,6-bis(3,5-dimethylphenyl)pyrazin-2-yltrifluoromethanesulfonate

Next, 4.80 g of 5-hydroxy-2,3-(3,5-dimethylphenyl)pyrazine which wasobtained in Step 1, 4.5 mL of triethylamine, and 80 mL of dehydrateddichloromethane were put into a three-necked flask, and the air in theflask was replaced with nitrogen. The flask was cooled down to −20° C.Then, 3.5 mL of trifluoromethanesulfonic anhydride was dropped therein,and stirring was performed at room temperature for 17.5 hours. Afterthat, the flask was cooled down to 0° C. Then, 0.7 mL oftrifluoromethanesulfonic anhydride was further dropped therein, andstirring was performed at room temperature for 22 hours to cause areaction. To the reaction solution, 50 mL of water and 5 mL of 1Mhydrochloric acid were added and then, dichloromethane was added, sothat a substance contained in the reaction solution was extracted in thedichloromethane. A saturated aqueous solution of sodiumhydrogencarbonate and saturated saline were added to thisdichloromethane for washing. Then, magnesium sulfate was added theretofor drying. After being dried, the solution was filtered, and thefiltrate was concentrated and the obtained residue was purified bysilica gel column chromatography using toluene:hexane=1:1 (volume ratio)as a developing solvent, to give an objective pyrazine derivative asyellow oil in a yield of 96%. A synthesis scheme of Step 2 is shown in(a-2).

Step 3: Synthesis of5-(4-cyano-2,6-dimethylphenyl)-2,3-bis(3,5-dimethylphenyl)pyrazine(abbreviation: Hdmdppr-dmCP)

Next, 2.05 g of 5,6-bis(3,5-dimethylphenyl)pyrazin-2-yltrifluoromethanesulfonate which was obtained in Step 2, 1.00 g of4-cyano-2,6-dimethylphenylboronic acid, 3.81 g of tripotassiumphosphate, 40 mL of toluene, and 4 mL of water were put into athree-necked flask, and the air in the flask was replaced with nitrogen.The mixture in the flask was degassed by being stirred under reducedpressure, 0.044 g of tris(dibenzylideneacetone)dipalladium(0) and 0.084g of tris(2,6-dimethoxyphenyl)phosphine were then added thereto, and themixture was refluxed for 7 hours. Water was added to the reactionsolution, and then toluene was added, so that the material contained inthe reaction solution was extracted in the toluene. Saturated saline wasadded to the toluene solution, and the toluene solution was washed.Then, magnesium sulfate was added thereto for drying. After being dried,the solution was filtered, and the filtrate was concentrated and theobtained residue was purified by silica gel column chromatography usinghexane:ethyl acetate=5:1 (volume ratio) as a developing solvent, to givean objective pyrazine derivative Hdmdppr-dmCP as white powder in a yieldof 90%. A synthesis scheme of Step 3 is shown in (a-3).

Step 4: Synthesis ofdi-μ-chloro-tetrakis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-κN]phenyl-κC}diiridium(III)(abbreviation: [Ir(dmdppr-dmCP)₂Cl]₂)

Next, 15 mL of 2-ethoxyethanol, 5 mL of water, 1.74 g of Hdmdppr-dmCP(abbreviation) which was obtained in Step 3, and 0.60 g of iridiumchloride hydrate (IrCl₃×H₂O) (produced by FURUYA METAL Co., Ltd.) wereput into a recovery flask equipped with a reflux pipe, and the air inthe flask was replaced with argon. After that, microwave irradiation(2.45 GHz, 100 W) was performed for an hour to cause a reaction. Thesolvent was distilled off, and then the obtained residue wassuction-filtered and washed with hexane to give a dinuclear complex[Ir(dmdppr-dmCP)₂Cl]₂ as brown powder in a yield of 89%. A synthesisscheme of Step 4 is shown in (a-4).

<Step 5: Synthesis of bis{4,6-dimethyl-2-[5-(4-cyano-2,6-dimethylphenyl)-3-(3,5-dimethylphenyl)-2-pyrazinyl-N]phenyl-κC}(2,2,6,6-tetramethyl-3,5-heptanedionato-κ²O,O′)iridium(III)(abbreviation: [Ir(dmdppr-dmCP)₂(dpm)])>

Furthermore, 30 mL of 2-ethoxyethanol, 0.96 g of [Ir(dmdppr-dmCP)₂Cl]₂that is the dinuclear complex obtained in Step 4, 0.26 g ofdipivaloylmethane (abbreviation: Hdpm), and 0.48 g of sodium carbonatewere put into a recovery flask equipped with a reflux pipe, and the airin the flask was replaced with argon. After that, microwave irradiation(2.45 GHz, 100 W) was performed for 60 minutes. Moreover, 0.13 g of Hdpmwas added thereto, and the reaction container was subjected to microwaveirradiation (2.45 GHz, 120 W) for 60 minutes to cause a reaction. Thesolvent was distilled off, and the obtained residue was purified bysilica gel column chromatography using dichloromethane and hexane as adeveloping solvent in a volume ratio of 1:1. The obtained residue wasfurther purified by silica gel column chromatography usingdichloromethane as a developing solvent, and then recrystallization wasperformed with a mixed solvent of dichloromethane and methanol to give[Ir(dmdppr-dmCP)₂(dpm)] which is the organometallic complex as redpowder in a yield of 37%. By a train sublimation method, 0.39 g of theobtained red powder was purified. The sublimation purification wascarried out at 300° C. under a pressure of 2.6 Pa with a flow rate of anargon gas at 5 mL/min. After the purification by sublimation, a redsolid, which was an objective substance, was obtained in a yield of 85%.A synthetic scheme of Step 5 is shown in (a-5).

Note that results of the analysis of the red powder obtained in Step 5by nuclear magnetic resonance spectrometry (1H-NMR) are given below.These results revealed that [Ir(dmdppr-dmCP)₂(dpm)], which is theorganometallic complex represented by Structural Formula (100), wasobtained in this synthesis example.

¹H-NMR. δ (CD₂Cl₂): 0.91 (s, 18H), 1.41 (s, 6H), 1.95 (s, 6H), 2.12 (s,12H), 2.35 (s, 12H), 5.63 (s, 1H), 6.49 (s, 2H), 6.86 (s, 2H), 7.17 (s,2H), 7.34 (s, 4H), 7.43 (s, 4H), 8.15 (s, 2H).

EXPLANATION OF REFERENCE

100L: liquid crystal element, 100E: light-emitting element, 101L, 101E:first electrode, 102L, 102E: second electrode, 103L: liquid crystallayer, 103E: EL layer, 104: alignment film, 105L: color filter, 105E:color filter, 106: polarizing layer, 107L, 107E, 108: light, 200R,200R′, 200R″: light-emitting element (red), 200G, 200G′, 200G″:light-emitting element (green), 200B, 200B′, 200B″: light-emittingelement (blue), 201: first electrode, 202, 202′: second electrode, 203R,203G, 203B, 203W: EL layer, 204R, 204G, 204B: EL layer, 207R, 207R′,207R″: light emission (red), 207G, 207G′, 207G″: light emission (green),207B, 207B′, 207B″: light emission (blue), 301: first electrode, 302:second electrode, 303: EL layer, 303 a, 303 b: EL layer, 304: chargegeneration layer, 311, 311 a, 311 b: hole-injection layer, 312, 312 a,312 b: hole-transport layer, 313, 313 a, 313 b: light-emitting layer,314, 314 a, 314 b: electron-transport layer, 315, 315 a, 315 b:electron-injection layer, 401: liquid crystal element, 402:light-emitting element, 403: conductive layer, 404: opening, 405: secondsubstrate, 407: conductive layer, 408: conductive layer, 409: liquidcrystal layer, 410: first element layer (display element layer), 411:second element layer (display element layer), 412: third element layer(driving element layer), 415: alignment film, 416: alignment film, 418:color filter, 419: insulating layer, 420: conductive layer, 421:conductive layer, 422: EL layer, 423: color filter, 424: polarizinglayer, 425: transistor, 426: transistor, 427: terminal portion, 501:circuit (G), 502: circuit (S), 503: display portion, 504: pixel, 505:conductive film, 506: position, 507: opening, 510: liquid crystalelement, 511: light-emitting element, 900: substrate, 901: firstelectrode, 902 a: first EL layer, 902 b: second EL layer, 903: secondelectrode, 904: charge generation layer, 905: substrate, 906: colorfilter, 911 a: first hole-injection layer, 911 b: second hole-injectionlayer, 912 a: first hole-transport layer, 912 b: second hole-transportlayer, 913 a: light-emitting layer (A), 913 b: light-emitting layer (B),913(b 1): first light-emitting layer (B1), 913(b 2): secondlight-emitting layer (B2), 914 a: first electron-transport layer, 914 b:second electron-transport layer, 915 a: first electron-injection layer,915 b: second electron-injection layer, 5101: light, 5102: wheel, 5103:door, 5104: display portion, 5105: steering wheel, 5106: gear lever,5107: seat, 5108: inner rearview mirror, 7100: television device, 7101:housing, 7103: display portion, 7105: stand, 7107: display portion,7109: operation key, 7110: remote controller, 7201: main body, 7202:housing, 7203: display portion, 7204: keyboard, 7205: externalconnection port, 7206: pointing device, 7302: housing, 7304: displayportion, 7305: icon indicating time, 7306: another icon, 7311: operationbutton, 7312: operation button, 7313: connection terminal, 7321: band,7322: clasp, 7400: mobile phone, 7401: housing, 7402: display portion,7403: operation button, 7404: external connection portion, 7405:speaker, 7406: microphone, 7407: camera, 7500(1), 7500(2): housing,7501(1), 7501(2): first screen, 7502(1), 7502(2): second screen, 7601:main body, 7602: display portion, 7603: arm, 9310: mobile informationterminal, 9311: display portion, 9312: display region, 9313: hinge,9315: housing

This application is based on Japanese Patent Application serial No.2016-159793 filed with Japan Patent Office on Aug. 17, 2016, the entirecontents of which are hereby incorporated by reference.

1. A display device comprising: a liquid crystal element; and alight-emitting element, wherein light obtained from the liquid crystalelement through a color filter has an NTSC area ratio of more than orequal to 20% and less than or equal to 60%, and wherein light emitted bythe light-emitting element has a BT.2020 area ratio of more than orequal to 80% and less than or equal to 100%.
 2. The display deviceaccording to claim 1, wherein the liquid crystal element is a reflectiveliquid crystal element, and wherein the light-emitting element comprisesan EL layer between a reflective electrode and a semi-transmissive andsemi-reflective electrode.
 3. The display device according to claim 1,wherein the liquid crystal element overlaps with the light-emittingelement.
 4. A display device comprising: a liquid crystal element; and alight-emitting element, wherein light obtained from the liquid crystalelement through a color filter has an NTSC coverage of more than orequal to 20% and less than or equal to 60%, and wherein light emitted bythe light-emitting element has a BT.2020 coverage of more than or equalto 75% and less than or equal to 100%.
 5. The display device accordingto claim 4, wherein the liquid crystal element overlaps with thelight-emitting element.
 6. The display device according to claim 4,wherein the liquid crystal element is a reflective liquid crystalelement, and wherein the light-emitting element comprises an EL layerbetween a reflective electrode and a semi-transmissive andsemi-reflective electrode.
 7. An electronic device comprising: thedisplay device according to claim 4; and an operation key, a speaker, amicrophone, or an external connection portion.
 8. A mobile phonecomprising: the display device according to claim 4; and an operationkey, a speaker, a microphone, or an external connection portion.
 9. Amobile information terminal comprising: the display device according toclaim 4; and an operation key, a speaker, a microphone, or an externalconnection portion.
 10. A display device comprising: a liquid crystalelement; and a first light-emitting element, wherein light obtained fromthe liquid crystal element has an NTSC coverage of more than or equal to20% and less than or equal to 60%, and wherein light emitted by thefirst light-emitting element has CIE 1931 chromaticity coordinates (x1,y1) where x1 is more than or equal to 0.130 and less than or equal to0.250 and y1 is more than 0.710 and less than or equal to 0.810.
 11. Thedisplay device according to claim 10, wherein the liquid crystal elementoverlaps with the first light-emitting element.
 12. The display deviceaccording to claim 10, wherein the liquid crystal element is areflective liquid crystal element, and wherein the first light-emittingelement comprises an EL layer between a reflective electrode and asemi-transmissive and semi-reflective electrode.
 13. The display deviceaccording to claim 10, further comprising, a second light-emittingelement, wherein light emitted by the second light-emitting element hasCIE 1931 chromaticity coordinates (x2, y2) where x2 is more than 0.680and less than or equal to 0.720 and y2 is more than or equal to 0.260and less than or equal to 0.320.
 14. The display device according toclaim 13, wherein the liquid crystal element overlaps with the secondlight-emitting element.
 15. The display device according to claim 10,further comprising, a third light-emitting element, wherein lightemitted by the third light-emitting element has CIE 1931 chromaticitycoordinates (x3, y3) where x3 is more than or equal to 0.120 and lessthan or equal to 0.170 and y3 is more than or equal to 0.020 and lessthan 0.060.
 16. The display device according to claim 15, wherein theliquid crystal element overlaps with the third light-emitting element.